ARIA Live Regions
ARIA live regions are a mechanism from the WAI-ARIA specification that makes screen readers announce dynamic content changes in the DOM automatically, without moving the keyboard focus – relevant among other things for WCAG success criterion 4.1.3 (status messages).
In practice
Typical use cases are automatically updating tickers, new chat messages without a page reload, the results of form validation, error messages or loading states. With aria-live="polite", the announcement waits until the screen reader is not reading anything else, whereas aria-live="assertive" interrupts the current speech output immediately and should therefore be used sparingly. Too many or too aggressive live regions quickly become disruptive – in case of doubt, "polite" is the gentler choice.