keytar
quite simply, it's a "portable keyboard". It's a small portable synthesizer (with keys of course) that has a handle similar to that of a guitar. The neck is usually kind of thick but still can be gripped by one hand. It may sport switches and buttons to alter the sounds being played. Keytars are convienient.
Jan Hammer of "Miami Vice" and Mahavishnu Orchestra fame glued a handle on his Probe keyboard for ease of walking around on stage while playing. This may be an example of an early keytar, but it wasn't called by that word yet.

Keytars first got notoriety in the 80s but are certainly not restricted to that decade by any means. Notable keytar players include Howard Jones AKA "Hojo", Jean Michel Jarre, the members of the Moog Cookbook and more. Hit videos by artists as diverse as Don Henley, Michael Jackson, Herbie Hancock, Janet Jackson , John Parr and even Shania Twain have featured backing musicians playing keytars.