Canvas is a term used to describe heavy weight plain weave fabrics. Canvas fabrics are classified by weight, similar to denim. The main difference between Canvas and Denim is the weave. Denim features a twill weave (diagonal lines running through the fabric) while canvas has a flat surface.
Mostly made from cotton, it can also be blended with other fibres such as linen. Historically canvas was made from Hemp fibres.
Canvas can be used for similar projects as denim such as jackets, trousers, dungarees, pinafores and skirts.
For some inspiration for this fabric check out this blog.