A combination is a forced sequence of moves — usually built around a sacrifice — that leads to a concrete gain such as checkmate or winning material.
What makes a combination different from ‘just playing well’ is that it is forcing and calculable. Each of your moves leaves the opponent with very few replies — checks, captures, and direct threats — so you can see the whole sequence through to a definite result.
Most combinations weave together the basic tactical motifs: a sacrifice to clear a line or deflect a defender, a check to force the king somewhere, then a fork, pin, or mate to cash in. The sacrifice is the spark; the forced follow-up is what makes it work.
Training combinations is the fastest way to gain rating. Solving puzzles teaches your eye to spot the loose piece, the exposed king, or the overworked defender that a forcing sequence can exploit.
A tactic is a single motif like a fork or a pin. A combination is a forcing sequence of several moves — often using one or more tactics plus a sacrifice — that ties them together into a concrete, calculated gain.
Very often, but not always. Many writers reserve the word ‘combination’ for forcing sequences that include a sacrifice; others use it for any forced tactical sequence that wins by calculation.
BetterChess is a practice tool — we make no guarantee you'll reach 1800 or any rating. Definitions are standard chess terminology; every diagram position is checked legal with the same engine the board runs.