In musical terms, a vamp can be defined as a repeating harmonic or rhythmic sequence, of usually two, four or eight bars. It can be based on a single harmony, a bass riff, or on a series of chord changes.
Vamps are everywhere these days, and have been for a good while. Listen to any contemporary charted pop tune and chances are the bulk of the tune is based on a vamp of some sort. Traditionally, a vamp might function as a song's intro. In our case, it functions as an improvisational vehicle often found at the end of a solo, or at the end of a standard tune, as well.