Under the gun (UTG)
Also called UTG
Under the gun (UTG) is the seat that has to act first before the flop — the player immediately to the left of the big blind.
The label points to a seat at the table, not a hand or a bet. Because the blinds are posted to the dealer button's left, the player just past the big blind is the one forced to make the opening decision before anyone else has acted preflop. The phrase borrows the feeling of being rushed or pressured into moving first.
It comes up every hand once cards are dealt: whoever is under the gun chooses to fold, call, or raise before the flop, and everyone else gets to respond to that choice. At a full table this is one of the earliest seats; at a very shorthanded table there may be no seat people call UTG at all (heads-up has none). Wit will usually point it out when it's your turn to lead the action.
Quick beginner note: acting first with the whole table still to speak is a tough spot, since any player behind you can wake up with a strong hand. A common habit is to play tighter from here and loosen up as you get closer to the button. Sitting first to act is one form of being out of position for the rest of the hand.
Example
At a 9-handed table, the chips post small and big blinds, and you're in the next seat with K♠ Q♠. You're under the gun, so before the flop you're the first to decide — you open for a raise to 3 big blinds and the remaining eight players act after you.