Explanation

Clearance is similar to a discovered attack or discovered check, in that you move one piece to reveal a threat of another piece. For a discovered attack or check that threat is a direct attack or check. For clearance, that threat can be checkmate, or some other tactics.

A clearing move can be especially strong if it is a forcing move, for example a capture, a check, or an attack. In that case, the opponent often cannot handle that forcing move, and the revealed threat at the same time.

In this level the revealed threat is trapping a piece. You move one piece out of the way for another piece to trap a piece on a subsequent move.

Examples

Black's knight on h5 has no squares but exchanging itself against the bishop on g3.
White can trade the bishop with 1.Bxb8, clearing the way for the g-pawn.
Black has to recapture with 1...Rxb8.
White can then trap the knight with 2.g4.

White played 1.Nxg5! to threaten checkmate on h7, clearing the way for the bishop. After 1...Qxg5 2.Bxb7 White had regained the piece and trapped the rook on a8. This is a typical motif in the Catalan and Queen's Indian openings.

Related motifs

With clearance, you move one piece to reveal a threat of another piece.
If that threat is a direct attack, it is called discovered attack, or discovered check.

You can also combine clearance with other motifs.