Definition of "angle shooting"
There is what is legal to do on a table of poker, there is what is illegal to do on a table of 4, and in between, there is the "angle shooting" which is a gesture that passes, but which is morally unacceptable. We speak of "angle shooting" when it is done maliciously in order to take advantage of it. When the gesture is done out of ignorance, it is simply a beginner making a mistake, but when it is done with full knowledge of the facts, it is "angle shooting".
Concrete example of "angle shooting"
A player bets on flop and you look at your chips. You act as if you want to raise a lot of chips. You play the player who wants to raise, but doesn't, and watch how your opponent reacts. On a table of poker you have to play honestly and play by the rules. Pretending" to raise or fold is borderline acceptable. You won't be penalized right away, but if you multiply your "angle shooting" moves, you may be banned from certain casinos. Think of "angle shooting" as the borderline between legal and illegal.