Bring in is a term used to denote the player who starts off the betting in any particular round. It is the first bet to fall in after everyone the big and the small blinds have put in their dues, with the cards having been distributed and all the antes already in the pile.
It is also a term used to denote a forced bet. In the first betting round, the player holding the worst upcard, whether the lowest or the highest, is responsible for bringing in the first bet for the game. The size of the bring in bet is not the same as a normal bet and can be a quarter or even up to a third of a small bet.
However, the bring in bettor always has the option of placing a complete bet if s/he thinks that the cards are good enough.
This form of forced betting normally occurs after the cards have been dealt out but no action has been made so far. The first person, normally selected in a single face-up card round on the initial deal, is forced to place the first bet of the game following which the game carries on normally and smoothly.
It is not uncommon to include this bring in amount along with the ante and the person with the worst, or best, up-facing card has to pay this amount. In low hand games, the player who got the highest card has to pay while in high hand games, it is the exact opposite.
The amount of the forced bet or bring in is determined beforehand and is usually a half or less of the smallest betting value. The bring in amount has also stood at the complete betting amount although that is an extremely rare scenario and isn’t followed much mainly due to the high paying nature of competitions.