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A short written description attached to an image that assistive software reads aloud, and that appears if the picture fails to load. It lets people who can't see the image still understand what it shows.

An invisible text label written into a page's code that tells a screen reader what a control does, used when an icon-only button or unlabelled field wouldn't otherwise make sense out loud.

On-screen text of the spoken words in a video, plus important sounds like [applause] or [door slams], so people who are deaf or hard of hearing can follow what's happening.

A set of colors chosen so people who can't easily tell certain hues apart — most often red and green — can still distinguish the elements, usually by also backing color up with labels, shapes, or patterns.

A measured comparison of how different text (or an icon) is in lightness from the background behind it, written as a ratio like 4.5:1. The bigger the number, the easier it is to read, especially for people with low vision.

The visible outline or highlight that shows which button, link, or field is currently selected when someone moves around a page with the keyboard instead of a mouse. Without it, keyboard users can't tell where they are.

The requirement that important things that aren't words — button edges, icons, form-field borders, chart bars, focus outlines — stand out enough from what's around them for people with low vision to see and use them.

The sequence in which a screen reader or the keyboard moves through a page's content. It should follow the logical, sensible order of the information, not the scattered way pieces happen to be placed on screen.

A design choice, respecting a person's device setting, that removes or softens animations and moving effects for users who feel dizzy, nauseous, or distracted by on-screen movement.

Software that reads what's on the screen aloud, or sends it to a refreshable Braille display, so people who are blind or have low vision can use a website or app without seeing it.

A link at the very top of a page — often hidden until you tab to it — that lets keyboard and screen-reader users jump straight to the main content, skipping past the repeated menus on every page.

The way text rearranges itself to fit a smaller screen or a larger zoom level, so a person can enlarge the words to read them without having to scroll sideways back and forth on every line.

The area of a button or link that actually responds to a tap or click. Making it large enough — commonly at least about 44 pixels — helps people with shaky hands or fat-finger taps on phones hit it reliably.

Text that is left off the visible screen but is still read by screen readers, used to give assistive-technology users context they'd otherwise miss — like labeling which of several "Edit" links goes with which item.