What if any differences are there between the terms layout and composition when talking about graphic design?
Layout is position, composition takes in to consideration stuff like color etc.
Imagine if this site decided to use a black background with white text instead of black text on white. It'd be the same layout, but a very different composition.
There is a difference that I think is best summed up by Robert Lane as seen on the Elements of Visual Design website:
Composition is the manner pieces or components are combined and arranged visually to tell a story. Proper composition considers alignment, grouping, placement, space, and visual flow within a layout. This layout can be any medium. Once a proper audience and purpose have been determined then composition, components, and concept can encompass that identified purpose allowing a successful design.
In other words, Composition can be seen as the elements that make up the design:
• the nature of something's ingredients or constituents; the way in which a whole or mixture is made up.
Whereas layout is the organization of said elements:
• the way in which the parts of something are arranged or laid out.