What is the origin of the term "Gig"?

"Gig" is a shortening of the the prefix "giga-". It is most often encountered in the term "gigabyte", a measure of storage capacity often abbreviated to "gig".

Originally, this came from the Greek word "qigantas", giant. However, is has been formally adopted as a prefix signifying 10^9 or 1,000,000,000. Thus a "gigasomething" is 1,000,000,000" somethings.

The water has been sometimes muddled in the field of disk storage, when "gig" sometimes means 2^30, which is slightly larger than 10^9, or some intermediate number.

In musical terms, it is an easy answer! New oRleans was a French-speaking colony. The word was transformed from "Gigue", meaning a dance (specifically, a French 18th-century dance), but the meaning probably was morphed to mean a musical performance of any type. Hence, "I have a gig, tonight" orginally meant "I am playing for a dance, tonight" and later meant "I have a musical engagement, tonight" (not necessarily a "dance", however)

There are several meanings of the word.
If you are referring to a job or work opportunity, I found this:

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

http://www.etymonline.com/index.php?search=GIG&searchmode=none

Likely comes from French gigue "a ball or dance".

so.....what IS the origin of gig then?? so far, i have read it came from an old english word meaning a fast carriage, a boat that captains used, etc. but how did we come to use it for stuff like performances, shows, etc.....?? anyone,....bueller.....?

Back in my rock and roll band days, the term gig, meant that we had an upcoming dance to perform. a gig.