Gamblers Anonymous

ATS = Against the Spread. Picking a team to win or lose getting or giving points.
Parlay = A single bet that links together two or more individual wagers and is dependent on all of those wagers winning. The benefit is that the payout are much higher.
Teaser = A Teaser bet is a parlay in which you take more points or lay fewer points than the line, thus adjusting the point spread in your favor. However, the payout is worse then a parlay because of this.
Prop = Prop bets are wagers made on an individual player or event. Prop bets can be placed on anything from how many points, rebound, or touchdowns certain players will score to which team will score the first in a specific game, etc.
O/U = Over/Under. This is a bet on the total number of points scored by both teams.
Live = A bet that is offered during live play, such as adjusted spreads, or whether someone will hit their next shot.

PER = Player Efficiency Rating; PER is a rating developed by ESPN.com columnist John Hollinger. In Hollinger's words, "The PER sums up all a player's positive accomplishments, subtracts the negative accomplishments, and returns a per-minute rating of a player's performance."
TS% = True Shooting Percentage; the formula is PTS / (2 * (FGA + 0.44 * FTA)). True shooting percentage is a measure of shooting efficiency that takes into account field goals, 3-point field goals, and free throws.
Usg% = Usage Percentage; the formula is 100 * ((FGA + 0.44 * FTA + TOV) * (Tm MP / 5)) / (MP * (Tm FGA + 0.44 * Tm FTA + Tm TOV)). Usage percentage is an estimate of the percentage of team plays used by a player while he was on the floor.
Adj. Plus/Minus (+/-) = Plus-Minus (+/-) results adjusted to account for both the teammates and the opponents on the floor with a player over the course of the season.