1.In poker, a term used to say how much money you have brought to the table at the beginning of your session.

2.In a poker tournament, buy-in is the amount of money that you pay towards the prize pool in order to enter the tournment.

3.any more money that is spent during the session is called a rebuy.

Got the covid-19 vaccine

To take part in the system. Or become mainstream.

The amount of money required to buy a spot in a poker tournament. It's also generally your starting amount of money in the tournament.

A nasty scam we used to pull on new employees when they got thier first full paycheck

A Poker term, when a player first sits down at the table and buys chips, it is called a "buy-in".