A sit and go tournament is a poker game between usually 6 to 10 players which takes between 20 and 60 minutes. They pay a fixed buy-in and get the same amount of poker chips. Whoever loses his chips is out of the tournament.
The last 3 or 2 players at the table win the prize money which is made of the buy-ins of all players. Almost every poker variant can be played as tournament.
p.s. This is a poker tournament in March 15, 2020.