There are two possible meanings to my knowledge: the one is a "gigabyte" relating a to a unit of measure of space in computers.
The second one is a concert, i.e. "will you be going to the gig later?"
"Gig is slang for a live musical performance. Originally coined in the 1920s by jazz musicians, the term, short for the word “engagement”, now refers to any aspect of performing, such as assisting with and attending musical performance. More broadly, the term “gigging” means having paid work, being employed."