Glossary

Short, sourced definitions for the technical terms that show up across Convertitive’s tools and methodology pages. Each term has its own page with examples and a link back to the tool it’s used in.

APR: Annual Percentage Rate. The yearly interest rate on a loan, inclusive of certain fees.
APY: Annual Percentage Yield. Yearly return rate accounting for compounding.
ASCII: American Standard Code for Information Interchange. 7-bit character encoding for English text.
Base64: A binary-to-text encoding using 64 ASCII characters. Standard for embedding binary data in text-only contexts.
Bessel's correction: Dividing by N−1 instead of N when computing sample variance, to remove sample-vs-population bias.
BigInt: JavaScript primitive for arbitrary-precision integer arithmetic.
BMI: Body Mass Index. The weight-to-height ratio used as a population-level screening metric.
Chroma subsampling: Storing colour at lower resolution than brightness, exploiting human vision's lower colour sensitivity.
DEFLATE: Lossless compression algorithm. The compression behind PNG, ZIP, gzip.
Gas Mark: British oven temperature scale. Mark 1 = 275°F = 135°C, then 25°F per mark.
Gwei: Ethereum's gas-price unit. 1 Gwei = 10⁻⁹ ETH = 10⁹ Wei.
IANA timezone: A canonical timezone identifier (like 'Europe/London') from the IANA Time Zone Database.
ISO 8601: The international standard for representing dates and times. YYYY-MM-DDTHH:MM:SSZ.
JWT: JSON Web Token. Three base64url-encoded segments: header.payload.signature.
Leap second: One-second adjustment to UTC to keep atomic time aligned with Earth's rotation.
Mid-market rate: The midpoint between buy and sell prices on the interbank currency market.
MIME type: Media type identifier telling a client what kind of data a payload contains.
hreflang: HTML attribute telling search engines which language and region a page targets.
Mortgage: A long-term, secured loan used to buy real estate. Standard amortising-loan math.
Planck constant: Fundamental physical constant (6.62607015 × 10⁻³⁴ J·s) that defines the kilogram.
SHA-256: Cryptographic hash function producing 256-bit digests. The modern standard.
Unicode: Universal character encoding standard covering every writing system in active use.
UTF-8: Variable-width Unicode encoding using 1-4 bytes per character. ASCII-compatible.
NIST: US National Institute of Standards and Technology. Publishes the canonical reference for US units in SI.
Percentile: The value below which a given percentage of observations fall. 90th percentile = beats 90% of the data.
Sample standard deviation: Square root of variance, using Bessel's correction (divide by N−1) to correct for sample-vs-population bias.
Satoshi: The smallest unit of Bitcoin. 1 BTC = 100,000,000 satoshi.
sRGB: Standard RGB — the default colour space of the web and most consumer displays.
UTC: Coordinated Universal Time. The reference clock every IANA timezone offset is measured against.
Wei: The smallest, indivisible unit of Ether. 1 ETH = 10¹⁸ Wei.
BMR: Basal Metabolic Rate. The energy your body burns at complete rest.
TDEE: Total Daily Energy Expenditure. BMR × activity multiplier.
Brannock device: Metal foot-measuring tool used by US shoe stores since 1925.
Mondopoint: International shoe sizing system. Foot length in millimeters (ISO 9407).
Interbank rate: The wholesale exchange rate at which large banks trade currencies with each other.
GPT token: The atomic unit of LLM input/output. ~4 English characters per token.
LLM: Large Language Model. Neural network trained to predict the next token.
Context window: Maximum tokens an LLM can process in a single inference (input + output combined).
Naegele's rule: Standard obstetric formula: estimated due date = LMP + 280 days.
Heron's formula: Compute triangle area from three side lengths without needing the height.
Gamut: The complete set of colours a colour space or device can represent.
Display P3: Wide-gamut RGB colour space used by modern Apple displays. ~25% more colour volume than sRGB.
Pantone: Proprietary spot-colour matching system. Each Pantone number is an exact ink formulation.
Kelvin: The SI base unit of temperature. Absolute zero is 0 K (−273.15°C).
DEXA: Dual-energy X-ray absorptiometry. Clinical gold-standard scan for body composition.
Fluid ounce: Volume unit. 1 US fl oz = 29.5735 ml. 1 UK fl oz = 28.4131 ml.
Decibel (dB): Logarithmic ratio unit. 10 dB = 10× power; 20 dB = 100× power.
Hertz (Hz): The SI unit of frequency. One cycle per second.
pH: Logarithmic measure of acidity, 0-14. Each unit is 10× the hydrogen ion concentration.
Density: Mass per unit volume. Why a cup of feathers weighs much less than a cup of flour.
Viscosity: How resistant a fluid is to flow. Water is 1 cP; honey is 10,000.
Maillard reaction: Chemical browning of amino acids + sugars at high heat. The flavour behind seared meat.
Autolyse: A rest in bread dough mixing — flour + water only, before yeast and salt.
ICC profile: Standardised description of a colour device's behaviour. Makes cross-device colour reproducible.
IEEE 754: The standard for floating-point arithmetic. Why 0.1 + 0.2 = 0.30000000000000004.
Lossy compression: Compression that discards information to save space. JPG, MP3, MP4.
Lossless compression: Compression that preserves every byte. PNG, FLAC, ZIP.
bps: Bits per second. Internet speeds, video bitrates. Different from Bps (bytes per second).
Kibibyte (KiB): Exactly 1024 bytes. The unambiguous binary alternative to 'kilobyte'.
BSON: Binary JSON. MongoDB's native storage format with extended types.
OTP: One-Time Password. Single-use code, typically 6 digits. The 2FA building block.
TOTP: Time-based One-Time Password (RFC 6238). Authenticator-app code derived from a shared secret + 30-second window.
CSRF: Cross-Site Request Forgery. Attack where a malicious site triggers authenticated requests using the victim's cookies.
XSS: Cross-Site Scripting. Injection of attacker JavaScript into a victim's view of a trusted site.
SAML: Security Assertion Markup Language. XML-based SSO standard, dominant in enterprise.
OAuth 2.0: Delegated authorization protocol. 'Allow this app to access my Google account without giving it my password.'
CORS: Cross-Origin Resource Sharing. Browser mechanism for controlled cross-origin requests.
CSP: Content Security Policy. HTTP header that whitelists allowed sources of scripts, styles, images.
SRI: Subresource Integrity. Pin a hash of an external script; refuse to run it if bytes don't match.
ETag: Entity Tag. HTTP cache-validation header containing a hash or version of the resource.
Referer: HTTP request header (famously misspelled) carrying the URL the user came from.
User-Agent: HTTP header identifying the client. Notoriously overgrown, lies about itself for backwards-compatibility.
SVG: Scalable Vector Graphics. XML-based vector image format. The right choice for logos and icons.
WebP: Modern web image format. Both lossy and lossless modes, full alpha, ~30% smaller than JPG at equivalent quality.
AVIF: AV1 Image File Format. ~20-30% smaller than WebP. Slow to encode, fast to decode.
Amortisation: The schedule of how a fixed-payment loan splits between interest and principal over time. Front-loaded with interest; principal reduction accelerates late.
Chroma: The colour's intensity or 'vividness' independent of lightness. The 'C' in OKLCH and the 'a/b' axes in OKLab. Distinct from saturation.
Chromaticity: The colour component of light, separate from its brightness. Plotted on the CIE 1931 chromaticity diagram; what defines a colour space's primaries.
Claim: A name/value pair in a JWT payload that asserts something about the bearer. Standard claims (iss, sub, exp, iat, aud) plus any custom application-specific ones.
Color temperature: The 'warmth' or 'coolness' of a light source, measured in Kelvin. 2700K is warm yellow tungsten, 5500K is daylight, 6500K is overcast daylight.
Correlation: A measure of how strongly two variables move together. Pearson's r runs −1 to 1; magnitude is strength, sign is direction. Correlation is not causation.
Delta E (ΔE): A numeric measure of perceptual colour difference. ΔE < 1 is invisible, ΔE > 5 is clearly different. Standard tool for evaluating colour reproduction.
Dimensional analysis: The technique of tracking units through equations to catch errors. If your answer for a distance comes out in seconds, the math is wrong.
DTI: Debt-to-income ratio. Total monthly debt service divided by gross monthly income. The 'back-end' half of the 28/36 mortgage rule.
Entropy (Shannon): A measure of randomness or unpredictability in bits. Passwords have entropy. Random numbers have entropy.
Equity (home): The portion of a property's value the owner actually owns, free of mortgage. Grows as the principal is paid down and as the property appreciates.
Escrow: Money or assets held by a third party on behalf of two transacting parties.
Gamma: The non-linear relationship between encoded pixel values and emitted light intensity. sRGB images apply ~2.2 gamma so that 8-bit values fit human perception.
Gas (Ethereum): Ethereum's unit of computational cost. Every operation has a gas cost; users pay gas × gas-price (in Gwei) for execution.
Geometric mean: The nth root of the product of n values. The right average for ratios, percentages, and compound growth rates.
Gluten: The protein network that forms in wheat dough when flour and water are mixed. Provides bread's elasticity and chew; absent in gluten-free flours.
Harmonic mean: The reciprocal of the mean of reciprocals. The right average for rates — speed, throughput, fuel economy averaged across legs of a trip.
Header (JWT/JWS): The first segment of a JWT or JWS, a base64url-encoded JSON object declaring the signing algorithm and key reference. Three to five well-known fields.
Hydration (baking): The ratio of water to flour in a dough, expressed as a percentage. Bread is typically 60-80% hydration; ciabatta and focaccia run higher.
Interquartile range: The spread between the 25th and 75th percentiles. Captures the middle 50% of a dataset and ignores outliers — where standard deviation gets distorted.
IP address: The numeric identifier of a device on a network. IPv4 (32 bits, dotted quads) and IPv6 (128 bits, eight hex groups) coexist; both name 'a host'.
JWE: JSON Web Encryption. A five-segment token format where the payload is actually encrypted, not just base64-encoded. Use when JWT contents must stay confidential.
JWS: JSON Web Signature. The signature framework JWT is built on. Carries any byte string as payload, not just JSON. Every JWT is a JWS; not every JWS is a JWT.
Kilogram: The SI base unit of mass. Redefined in 2019 to be based on Planck's constant rather than a physical platinum-iridium artifact.
Latency: The time delay between a request and a response. The 'p99 latency' that engineers obsess over is the 99th percentile of response times.
LTV: Loan-to-value ratio. The mortgage balance divided by the property's market value. The single number lenders use to set rates, fees, and PMI eligibility.
Mean: Arithmetic mean — the sum of values divided by their count. The most common 'average'. Sensitive to outliers; median is the robust alternative.
Median: The middle value of a sorted list. Robust to outliers — half the data is below, half above. Where the mean misleads, the median usually doesn't.
Meter: The SI base unit of length. Defined since 1983 as the distance light travels in vacuum in 1/299,792,458 of a second.
Mode: The most frequent value in a dataset. The only 'average' that works for categorical data. Bimodal and multimodal distributions have more than one.
Mole: SI base unit of amount of substance. One mole = 6.02214076 × 10²³ particles — atoms, molecules, ions, whatever you're counting.
Percent encoding: URL encoding — the % followed by two hex digits scheme that escapes reserved and non-ASCII characters in URLs. Defined in RFC 3986.
PITI: Principal, Interest, Taxes, Insurance. The four components of a typical mortgage monthly payment and the figure lenders use in the 28/36 affordability rule.
Principal: The amount borrowed (or invested) before interest. The unpaid balance of a loan at any point in time.
Proof of stake: The consensus mechanism that replaced proof-of-work on Ethereum and most modern blockchains. Validators stake capital; bad behaviour costs the stake.
Regression: Fitting a model that predicts one variable from one or more others.
Second: The SI base unit of time. Defined since 1967 as 9,192,631,770 oscillations of a specific caesium-133 atomic transition.
Unix timestamp: Seconds since 1970-01-01 00:00:00 UTC. The lingua franca for time in computing.
Variance: The mean of squared deviations from the mean. Standard deviation's cousin without the final square root — squared units, additive across independent sources.
Weighted average: An average where some values count more than others. GPA, interest-rate blends, election polling, and ETF returns are all weighted averages.
Z-score: How many standard deviations a value is from the mean. The unit that lets you compare a 75 on a math test to a 68 on a French test fairly.