Canvas
The web page's drawing surface, where a tool paints pixels with code.
See it in Pixel art editor. Draw anything: every square lands on the page's canvas.
In plain words
A web page is mostly text and boxes. The canvas is a box made for drawing. Code tells it what to paint: lines, shapes, pictures or single pixels. It can be redrawn many times a second, which is how games and animations run in a browser. Every tool in the lab draws its picture on a canvas.