Wireframes are an extremely flexible tool for an interaction designer. At their most basic, they are simple sketches outlining page content, hierarchy, and user interface elements, and can be part of collaborative sessions with the entire design team.
Medium-fidelity wireframes can be used to gain consensus on data requirements, validations, and copy requirements.
At the other end of the spectrum, interactive wireframe prototypes can show rich elements that are often executed with HTML5, DHTML, JavaScript or Flash. These include any asynchronous page refreshes, moving elements, error handling, dynamic forms, etc.
This wireframe uses some existing assets such as imagery and a logo.