What is the name of the stand where painters hold their canvases?

An easel is a structure built to support an artist’s canvas. Easels are also commonly used to display finished works of art. Useful in many situations for many reasons, the easel, in all its forms, is a very old invention. Easels are formally recorded as far back as the first century CE when Pliny the Elder wrote about a large panel being painted on by an artist who had propped it up on what could have only been one of the first easels. Pliny the Elder was the accomplished writer of the book Natural History, which is considered to house nearly all of the ancient knowledge that preceded him.

Source: Easels by Amron