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 (Decoy, Clearance, Deflection, Undermining, Interference, X-ray attack).

Decoy is a tactic of luring a piece, usually the king or queen, onto a particular square through the means of a sacrifice on that square, from which the piece's new placement can be exploited to obtain an advantage.
Clearance is a tactical motif which involves a square on the chessboard being vacated to open up lines of attack.
Deflection is a tactic that forces an opposing piece to leave the square, rank or file it occupies, thus exposing the king or a valuable piece.
Undermining is a chess tactic in which a defensive piece is captured, leaving one of the opponent's pieces undefended or under-defended. The opponent has the unpalatable choice of recapturing or saving the undefended piece.
Interference occurs when the line between an attacked piece and its defender is interrupted by sacrificially interposing a piece.
X-ray attack is a tactic where a piece either: indirectly attacks an enemy piece through another piece or pieces, or defends a friendly piece through an enemy piece.