flash

a pair of opposing changes in relative luminance (opens in a new tab) that can cause seizures in some people if it is large enough and in the right frequency range

Note 1: See general flash and red flash thresholds (opens in a new tab) for information about types of flash that are not allowed.

Note 2: See also blinking (opens in a new tab).

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