Canvas size
From The Glossary of Digital Photography
(1) The size of the work area when working on an image in a software program. The work area often has the same dimensions as the image, but that is not necessary. The canvas size can be enlarged without changing the size of the image. (2) A command in Photoshop to change the canvas size. The canvas is often enlarged so that the borders can be stretched with cloning or by adding graphics around the borders of the image.
