Accessibility

Anything that can be identified by a Uniform Resource Identifier 

A device (hardware and software) that interprets voice markup languages to generate voice output, interpret voice input, and possibly accept and produce other modalities of input and output.

Content consisting exclusively of one or more visual tracks presented concurrently or in series.

Content rendered through a graphical viewport.

The user agent renders content through one or more viewports.

Style property values that come from user interface settings, user style sheets, or other user interactions.

1. the user agent user interface, i.e., the controls (e.g., menus, buttons, prompts, and other components for input and output) and mechanisms (e.g., selection and focus) provided by the user agent ("out of the box") that are not created by content.
   AND
2. the "content user interface," i.e., the enabled elements  that are part of content, such as form controls, links, and applets.

Style property values applied in the absence of any author or user styles.

1. The software and documentation components that together, conform to accessibility requirements. This is the most common use of the term in this document and is the usage in the checkpoints.
2. Any software that retrieves and renders Web content for users. This may include Web browsers, media players, plug-ins, and other programs — including assistive technologies— that help in retrieving and rendering Web content.

A text equivalent of audio information (e.g., an audio-only presentation or the audio track of a movie or other animation).

It provides text for both spoken words and non-spoken sounds such as sound effects. Text transcripts make audio information accessible to people who have hearing disabilities and to people who cannot play the audio. Text transcripts are usually created by hand but may be generated on the fly (e.g., by voice-to-text converters). 

Any stylistic effect that the user agent may apply to visually rendered text that does not affect the layout of the document (i.e., does not require reformatting when applied or removed).

Text decoration mechanisms include underline, overline, and strike-through.

<a href='#main_content'>Skip navigational links</a>...

...<a name='main_content'></a>

The meaning of something as understood by a human, defined in a way that computers can process a representation of an object, such as elements and attributes, and reliably represent the object in a way that various humans will achieve a mutually consistent understanding of the object.

User interface events, changes to content, loading of content, and requests from the operating environment.

Text equivalents (e.g., text equivalents for images, text transcripts for audio tracks, or collated text transcripts for a movie) and non-text equivalents(e.g., a prerecorded audio description of a visual track of a movie, or a sign language video rendition of a written text).