1) Wireframes are visual representations of interfaces used to communicate structure, content, hierarchy, functionality, and behavior to help formalize and test interface design ideas.
2) Paper prototyping allows designers to create inexpensive mockups of interfaces to identify problems and test usability by modeling different interface states that can be handed to users.
3) Usability testing with paper prototypes involves presenting users with paper "screens" and having them perform tasks while designers observe, take notes, and identify required changes based on user feedback and confusion points.