Here's below a short glossary about digital accessibility:

A11Y

Short for ‘‘accessibility’’ (there are 11 letters between ‘‘a’’ and ‘‘y’’). Accessible web content is usable by all people, regardless of physical or developmental abilities or impairments. Web accessibility uses the principle of universal design to make websites, applications, and content that is usable by persons with disabilities who may or may not be using assistive technologies to access the site.

ARIA

An acronym of Accessible Rich Internet Application, it's a set of roles and attributes to make web content more accessible for people with disabilities. These attributes communicate role, state and property to assistive technologies via accessibility APIs implemented in the accessibility tree in modern browsers.

Disability

Definitions for the term disability vary widely, arising from medical or social perspectives. Commonly accepted disabilities include (but are not limited to) impairment of one or more senses, cognitive disabilities, and mobility limitations.

Screenreader

A software application that attempts to identify and interpret what is displayed on the screen, translating the information usually to speech. Screen readers are relied on by people with no functional vision, but software that reads out on-screen content may also be used by people who have difficulty reading, because of a visual or cognitive impairment. VoiceOver for Apple is the screen reader primarily used on this campus. You can also use NVDA (free and open source tool) or Jaws.

Semantic HTML

HTML semantics provide accessibility information about page structure for assistive technologies like screen readers and speech recognition software. You can use HTML to give content structure by identifying things like headings, lists, paragraphs and buttons. Writing semantic code is about choosing the most appropriate element to create your web content.

VPAT

The Voluntary Product Accessibility Template (VPAT) is a document which evaluates how accessible a particular product is according to the Section 508 Standards. It is a self-disclosing document produced by the vendor which details each aspect of the Section 508 requirements and how the product supports each criteria.
VPATs are required by some buyers before a purchase is made.

WCAG

Web Content Accessibility Guidelines, created in 1999 by the W3C which created Web Accessibility Initiative (WAI) to improve the accessibility of the internet. WCAG is the most widely adopted standard for creating accessible web content. Globally, organizations strive to meet the standards of web accessibility known as WCAG 2.2 AA (55 success criteria).

It may be helpful to think about accessibility as a continuum.
Providing access to everyone is the ultimate goal, and accommodations and accessible design work together to create inclusion.