In the past, it was called "moonlighting." It was a job you did to earn extra money, in addition to your fulltime job.
These days, it's referred to as a "side-hustle," and more people have one. In fact, a report by Bankrate estimates 44 million Americans are earning extra cash on the side.
The research shows that most people with a side-hustle work at it every month, and more than a third of them pocket an additional $500 or more. The younger you are, the more likely you are to be consistent with your outside work.
However, Millennials tend to earn less on the side than do older employees. Among Millennials, only 19% with a side-hustle earn $500 or more per month.
Younger Baby Boomers are the most likely age group to earn $1000 a month or more on the side.
Created out of need
Side-hustles most likely gained popularity in the years after the financial crisis, when pay raises were few and far between. Of those earning extra money on the side, 54% say they use it to help pay expenses, which tend to go up, even when pay doesn't.
"A side hustle can be a great way to help pay the bills or pad your savings account on your own schedule," said Sarah Berger, the Cashlorette at Bankrate.com. "It's important to be smart about any extra income you earn. Pay down debt and take care of your monthly expenses first before adding anything to your shopping cart."
The rise of the so-called "gig economy" has also produced more side hustle opportunities. Many businesses have found it more cost effective to hire temporary contract workers than add to the payroll.
Internet venues have also created opportunities for people to start a sideline, home-based business to earn a little extra cash.
Forbes recently identified several side-hustles that aren't that hard to do. They include giving online English lessons on Skype, using your Instagram account to market products and services, and even refurbishing used electronics, if you have that ability.