The act of using various underhanded, unfair methods to take advantage of inexperienced opponents. The difference between an "angle shooter" and a "cheater" is only a matter of degree. What a cheat or thief does is patently against the rules; what an angle shooter does may be marginally legal, but it's neither ethical nor gentlemanly. Nor is it in the spirit of the game.
A common tactic of someone angle shooting is, to bank on the misinterpretation of actions by other players at the table.
Some well-known angle shoots have now been banned. While there weren't rules against them at first, the tournament organizers have now come up with rules specifically banning them.
Example of Angle Shooting #1:
Player A bets the river for 100,000. Player B makes a motion with his chips like he wants to call, to which Player A reacts. Player B now has additional information.
Example of Angle Shooting #2:
A player finds pocket aces and says "five" while tossing in a 5,000-chip in the 100/200 level. The dealer notifies the player that saying "five" constitutes a raise to 5,000, and not 500. That player now acts confused, to trick the table into believing he meant to raise to 500. This is technically not against the rules, but it's both unethical and against the spirit of the game.
Angle shooting used in a sentence
"Wow, I can't believe he did that. He really tried to angle shoot you!"