Yes a jobber is a guy who usually loses all the matches. He is often used in squash matches to push other stars.
Sometimes, jobbers were also made to mimic other superstars in a comic way, e.g., WWE created the Gillberg character who was a jobber - as a spoof of WCW's dominant star Goldberg. He tried to keep a similar French cut and bald head, dressed similarly although he was much thinner and smaller, and walked to the ring similar to Goldberg with security accompanying him backstage, and did some parodies after the pyrotechnics in his entrance.
Sometimes, credible superstars are also made to job at times (e.g., a recent match between Sheamus and Daniel Bryan in which Sheamus squashed him - it was berated by many superstars on Twitter and many wrestling websites). Although, those are one-off scenarios. Usually the IWC (Internet Wrestling Community) often uses the term job more commonly but don't fall into that trap (e.g., when Undertaker lost cleanly to Kane at their No Holds Barred match this year - some would say that Undertaker jobbed to Kane, but that is wrong and it does not make him a jobber by any means).
There have been cases where jobbers went through a gimmick change to suddenly become great and memorable superstars - e.g., Glen Jacobs (Kane) used to be a jobber as Isaac Yankem DDS earlier and later he was made the fake Diesel, which didn't work either; but suddenly he was repackaged as Kane and the rest is history.