Define: Sketch, Wireframe, Mock-up and Protoype

• Sketch Any representation of a user interface as a drawing.
• Wireframe A static representation of a user interface where the individual elements are at least roughly where they are supposed to go, at their supposed sizes.
• Mock-up A (usually static) representation of a user interface where decorations like shadows and colors are introduced.
• Prototype Any representation of a product that is not the final product.

(Design to Use by Lukas Mathis)