I found a new job, and one of my friends said this to me. I know what she means though i have no idea what gig is. The meaning is congrats on your new endeavor, isn't it?

Is 'gig' an abbreviation? how does this expression come from? thanks a lot.
Gig was originally musical work, I believe. Let me check.

Yes indeed: from the Online Etymological Dictionary--

gig (2) "job," first used by jazz musicians, attested from 1915 but said to have been in use c.1905; of uncertain origin.


Function: noun
Inflected Form(s): -s
Etymology: origin unknown

1 : a single engagement; especially : ONE-NIGHT STAND<graduate work in music, with as much sideline work, as many gigs, as the student can find time to develop his jazz skills -- Barry Ulanov>
2 : JOB