Definition: Format refers to the size, shape and orientation of your paper or canvas. Portrait format means the paper is oriented with the shorter sides horizontal, while landscape describes paper with longer horizontals.
Format is independent of subject: you could have a portrait drawing on landscape-format paper, or you could do a landscape drawing on portrait-format paper.
Non standard formats are occasionally used, such as square, or more rarely, round. However, these formats create compositional challenges so are usually only chosen for a specific reason.
In Computer Aided Drafting, format may refer to the method of data processing used to create the drawing, either as vectors (lines) or as raster data (dots). It may also refer to file format, such as GIF or JPEG.
Examples:
"The world just does not fit conveniently into the format of a 35mm camera. " - W. Eugene Smith
