Turn
The fourth community card, dealt after the flop betting round. Also called fourth street.
After one more burn card, the dealer places the turn next to the flop. In fixed-limit games the bet size usually doubles on the turn, which is why it is sometimes called the "big street".
The turn is where many draws either complete or fall one step closer to missing. With one card to come, the rule of 2 and 4 says multiply your outs by two to estimate your chance of hitting.
Example
Board J83, turn 9: anyone holding T or Q-T now has a straight.