A tactic is a sequence of moves that limits the opponent's options and may result in tangible gain. Tactics are usually contrasted with strategy, in which advantages take longer to be realized, and the opponent is less constrained in responding.
With this application you can solve thousands of chess tactic puzzles grouped by theme (Attacking F7/F2, Exposed king, Kingside attack, Queenside attack, Sacrifice).

Attacking F7/F2 is a tactic or threat that involves the targeting of the opponent's weakest square. Often f7 and f2 are referred to as the weakest squares on a chessboard because they are protected only by the king at the start.
Exposed king is a king that doesn't have the necessary protection against checks and threats from enemy pieces.
Kingside attack is an attack of the opponent's king, after they castled on the king side.
Queenside attack is an attack of the opponent's king, after they castled on the queen side.
Sacrifice is a move giving up a piece with the objective of gaining tactical or positional compensation in other forms.