SVG
In plain terms
A vector image format defined in XML that scales without quality loss.
Going deeper
SVG describes graphics as shapes and paths in markup, so they scale crisply at any size and can be styled and animated with CSS/JS. It's resolution-independent.
Under the hood
Retained DOM elements make SVG scriptable and accessible; better than canvas for scalable, interactive vector graphics.
Examples
Icons, logos, charts, animations, responsive illustrations.
Think of it like...
Like a recipe for a drawing rather than a fixed photo, redrawn perfectly at any size.