Where designers start brainstorming layouts and designs with a pencil in hand, producing doodles that may be incomprehensible to anyone else, a composite, or comp for short, takes your thumbnail sketch and makes it presentable for a client to see.

Comps can be hand-drawn if they are done so neatly and professionally. Once you've thumbnailed they can be scanned to Photoshop, Illustrator, etc.

Though comps are not finished designs, they are the necessary middle step between thumbnail sketches and the final visual design.