O
Odds
The chances of making a hand compared to not making it

Off Suit
Two cards, typically hole cards, that have different suits

Omaha
A version of poker similar to Hold `Em, but with four hole cards

Omaha Hi/Lo
A version of poker similar to Hold `Em, but with four hole cards and the pot split between the best high and low hands

On Board
The cards that make up the community cards

One-Gap
A Hold `Em starting hand with two cards two apart in rank, e.g. 8and 6 or T and Q

Open Ended Straight Draw
Four cards to a straight where a card ranking above or below the run will complete the hand

Out
A card that will improve your hand

Outdraw
To improve your hand from a losing hand to a winning one

Overcard
A card higher than any card on the board, or any card on the board higher than your pocket pair

Overpair
A card higher than any card on the board, or any card on the board higher than your pocket pair