A gig means a work done for short period of time.
A gig economy is a market place for workers who take up multiple projects with multiple employers without being committed wholly to a single employer.
It is a market where individuals works independently without being bound in a long term contract with a single employer.
People who work on gigs are known as giggers or freelancers.
Gig economy is gaining traction from both companies and workers.
Companies who employ giggers are at advantage because they don’t have to provide additional benefits like healthcare or transportation to these giggers.
Giggers enjoy the benefit of flexible working hours as well as work from home.
You can read https://www.feedough.com/what-is-gig-economy/ this article for a more detailed explanation.