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OESD
• Open Ended Straight Draw

Offsuit
• Cards of a different suit.

Omaha
• A game in which each player is dealt four down cards with five community cards. To make your hand, you must play two cards from your hand and three from the board.

On the Button
• Being the last player to act in a betting round. Dealer's Position.

On the Come
• A situation where the player does not yet have a complete hand.

One-Gap
• A hold'em starting hand in which the two cards are two apart in rank. Examples: J9s, 64.

One-Way Straight
• Or One-End. A four-card straight open only on one end, such as jack, queen, king, ace.

Open
• To make the first bet.

Open Ended Straight Draw
• Four consecutive cards whereby one additional (consecutive) card is needed at either end to make a straight. Abbreviated as "OESD"

Opener
• The player who made the first voluntary bet.

Option
• A Live Blind made in the dark before the cards are dealt. If no one raises, the "option" player may raise the pot.

Out of Position
• Being in a hand where there are players to act after you. Typically they have a strategic advantage over you.

Outdraw
• When one person beats his or her opponent by drawing a better hand.

Outs
• The number of cards left in the deck that will improve your hand.

Over the Top
• When you re-raise another player’s raise, usually unexpectedly.

Overcall
• To call a bet after one or more others players have already called.

Overcard
• A card in your hand higher than any card on the board.

Overpair
• A pocket pair higher than any of the cards on the board.