What is Canvas and what is it used for?

It is used for upholstery, table cloth, waxing, hair removal, painting etc.
Canvas is an extremely heavy-duty plain-woven fabric used for making sails, tents, marquees, backpacks, and other items for which sturdiness is required. It is also popularly used by artists as a painting surface, typically stretched across a wooden frame. It is also used in such fashion objects as handbags and shoes.
Modern canvas is usually made of cotton or linen, although historically it was made from hemp. It differs from other heavy cotton fabrics, such as denim, in being plain weave rather than twill weave. Canvas comes in two basic types: plain and duck. The threads in duck canvas are more tightly woven. The term duck comes from the Dutch word for cloth, doek. In the United States, canvas is classified in two ways: by weight (ounces per square yard) and by a graded number system. The numbers run in reverse of the weight so a number 10 canvas is lighter than number 4.
Canvas has become the most common support medium for oil painting, replacing wooden panels. One of the earliest surviving oils on canvas is a French Madonna with angels from around 1410 in the Gemäldegalerie, Berlin. However, panel painting remained more common until the 16th century in Italy and the 17th century in Northern Europe. Mantegna and Venetian artists were among those leading the change; Venetian sail canvas was readily available and regarded as the best quality.
It has become popular to use the myriad of stretched canvasses sizes and shapes for unconventional creative expression. Artists can create miniature works on business card sized stretched canvas and use them as trading cards to make connections with other artists. Many artists use canvas for altered art pieces as well as for scrapbook pages—because stretched canvas is available in many sizes, from miniatures to wall size, it is used for decoupage and needlework projects, made into lamps, or painted simply for home decor.