viewport

object in which the user agent (opens in a new tab) presents content

Note 1: The user agent presents content through one or more viewports. Viewports include windows, frames, loudspeakers, and virtual magnifying glasses. A viewport may contain another viewport (e.g., nested frames). Interface components created by the user agent such as prompts, menus, and alerts are not viewports.

Note 2: This definition is based on User Agent Accessibility Guidelines 1.0 Glossary (opens in a new tab) [UAAG10 (opens in a new tab)].

Source: WCAG 2.2 definition of “viewport” (opens in a new tab) (W3C)