Generally a homeless nomad
who wanders the face of the planet taking one shit job
after another on because the permanent employee
s in the office that hired him/her are either too lazy or too smart to do that particular piece of work.
To look at it another way, someone who is so technically skilled that to place them in just one office would be a waste to the world. Also they are generally so smart in skill areas where there is a shortage that most businesses cannot afford to keep them on for long periods of time and thus hire them for three or six months at the most, or until someone in the Finance Department realises just how much is being paid for one guy.
I like the second definition better but then I am a contractor so maybe my viewpoint is skewed.