Glossary

Base64

A way of encoding binary data as text using 64 safe characters, so it can travel in places that expect text, such as URLs, emails or JSON. It makes data about a third larger and is an encoding, not encryption: anyone can decode it. Try it →

Board foot

A unit of lumber volume equal to a piece 12 in × 12 in × 1 in, or 144 cubic inches. Board feet = thickness (in) × width (in) × length (ft) ÷ 12, using nominal or actual sizes as the seller specifies. Try it →

Box shadow

A CSS property that draws one or more shadows around an element’s box, defined by horizontal and vertical offset, blur radius, spread and colour. Layering several soft, low-opacity shadows usually looks more natural than a single dark one. Try it →

Brotli and gzip

Two lossless compression formats that web servers use to send text files such as HTML, CSS and JavaScript in fewer bytes. The browser announces what it supports, and the server picks one; Brotli usually produces smaller files than gzip. Try it →

BTU

British thermal unit: the energy needed to raise one pound of water by one degree Fahrenheit. Heating and cooling equipment is rated in BTU per hour, and 12,000 BTU/h equals one “ton” of air-conditioning capacity. Try it →

Colour stop

A colour placed at a position along a CSS gradient, for example red 40%. The browser blends between neighbouring stops; two stops at the same position create a hard edge instead of a fade, which is how stripes and pie charts are drawn. Try it → · Read the guide

Contrast ratio

A measure from 1:1 to 21:1 of how different two colours are in brightness, calculated from their relative luminance. WCAG 2.2 asks for at least 4.5:1 for normal text and 3:1 for large text so that people with low vision can read it. Try it →

CSS box model

The way a browser sizes every element: the content area, then padding, then border, then margin. With box-sizing: content-box (the default) width sets only the content; with box-sizing: border-box, width includes padding and border, which makes layouts easier to predict. Try it →

CSS gradient

An image generated by the browser that blends two or more colours, written with linear-gradient(), radial-gradient() or conic-gradient(). Because it is an image, it goes in background-image rather than background-color, and it costs no network request. Try it → · Read the guide

CSS grid

A two-dimensional CSS layout system (display: grid) that places items into rows and columns at the same time. Tracks are defined with grid-template-columns and grid-template-rows, and the fr unit shares out the remaining free space. Try it →

CSS specificity

The rule that decides which CSS declaration wins when several target the same element. It is compared as three counts – IDs, then classes, attributes and pseudo-classes, then element types – and only when those tie does the later rule in the stylesheet win. Try it →

Cubic Bézier easing

A timing function, cubic-bezier(x1, y1, x2, y2), that sets how a CSS transition or animation speeds up and slows down. The four numbers place two control points on a curve from 0,0 to 1,1; keywords such as ease-in-out are presets of it. Try it →

Cubic yard

A volume of 3 ft × 3 ft × 3 ft, which is 27 cubic feet (about 0.76 m³). Ready-mix concrete, gravel and soil are usually ordered by the cubic yard in the United States, so slab volumes in cubic feet are divided by 27. Try it → · Read the guide

Drywall sheet

A panel of gypsum board, commonly 4 ft wide and 8, 10 or 12 ft long in North America, fixed to studs or joists to form walls and ceilings. Estimates divide the wall and ceiling area by the sheet area and add a waste allowance. Try it →

Flexbox

A one-dimensional CSS layout mode (display: flex) that arranges items in a row or a column and distributes space between them. justify-content aligns items along the main axis, align-items across it, and flex-grow, flex-shrink and flex-basis control how each item sizes. Try it →

Footing

The widened concrete base at the bottom of a foundation wall, post or column that spreads the building’s load over enough soil to support it. Footing size and depth are set by local building codes, soil conditions and the load above. Try it →

JSON

JavaScript Object Notation: a plain-text format for structured data made of objects, arrays, strings, numbers, true, false and null. It is the usual format for web APIs and configuration files, and it does not allow comments or trailing commas. Try it →

JSON Web Token (JWT)

A compact, URL-safe token made of three Base64URL parts – header, payload and signature – used to pass claims such as a user ID between systems. The payload can be read by anyone; the signature only proves it was not changed. Try it →

Media query

A CSS condition that applies styles only when it is true, such as @media (min-width: 768px) or @media (prefers-reduced-motion: reduce). Media queries make one stylesheet adapt to screen size, input type and user preferences. Try it →

Minification

Shrinking code without changing what it does: removing whitespace and comments and, for JavaScript, shortening local variable names. Minified files download faster; compression such as gzip or Brotli is then applied on top by the server. Try it →

OKLCH

A CSS colour space that describes a colour by perceptual lightness (L), chroma (C, colourfulness) and hue (H). Because equal steps look roughly equal to the eye, it is useful for building colour palettes and smooth gradients, written as oklch(70% 0.15 250). Try it → · Read the guide

Percentage change

How much a value has grown or shrunk relative to where it started: (new − old) ÷ old × 100. Going from 50 to 60 is a 20% increase, but going back from 60 to 50 is a 16.7% decrease, because the starting value differs. Try it →

Percentage point

The plain difference between two percentages. A rate rising from 4% to 5% has gone up by one percentage point, which is a 25% increase in the rate itself – the two phrases describe the same change in different ways. Try it →

R-value

A material’s resistance to heat flow: the higher the R-value, the better it insulates. R-values of layers in a wall or roof add up, and required values depend on the climate zone in the local energy code. Try it →

Rebar

Steel reinforcing bar cast inside concrete to carry tension, which concrete resists poorly. In the US, bar sizes are numbered in eighths of an inch of diameter, so a #4 bar is 4/8 = 1/2 inch across. Try it →

Regular expression

A pattern language for finding and replacing text, such as \d{3} for three digits. Regular expressions are built into JavaScript and most programming languages; flags like g (global) and i (ignore case) change how a pattern matches. Try it →

rem unit

A CSS length relative to the root element’s font size. With the browser default of 16 px, 1rem equals 16px, so sizes in rem scale when a user increases their default text size, which helps accessibility. Try it →

Rise and run (stairs)

The rise is the height of one step and the run (tread depth) is its horizontal depth. Total rise divided by the number of risers gives the step height; building codes set maximum rise and minimum run, so check the code that applies. Try it →

Roof pitch

The steepness of a roof, written as rise over a 12-inch run in the US (for example 6/12) or as an angle in degrees. A 6/12 pitch rises 6 inches for every 12 inches of horizontal distance, about 26.6 degrees. Try it →

Slump (concrete)

A measure of how workable fresh concrete is: the distance a cone-shaped sample sags after the mould is lifted, measured in inches or millimetres. Higher slump means wetter, more fluid concrete; the required slump is set by the job specification. Try it → · Read the guide

UUID

A universally unique identifier: a 128-bit value written as 32 hexadecimal digits in five groups. Version 4 UUIDs are random; version 7 UUIDs start with a timestamp, so they sort by creation time, which suits database keys. Try it →

Waste factor

An extra percentage added to a material estimate to cover offcuts, spillage, uneven ground and breakage. Calculators let you choose it because the right allowance depends on the material, the shape of the job and how experienced the installer is. Try it → · Read the guide

Educational content only. It explains how things work in general and is not financial, tax or legal advice for your situation.