A cover band (or covers band) is a band that plays only cover songs. Most wedding bands can be considered cover bands. Another term is party band.
Cover bands typically play a mix of songs from different decades and different styles. Some cover bands play material from particular decades, for example a 1980s cover band. Others focus exclusively on a single group, and are called tribute bands: it is not uncommon to find Led Zeppelin cover bands, Pink Floyd cover bands, or U2 cover bands.