A block is a defensive tactic in chess in response to an attack, consisting of interposing a piece between the opponent's attacking piece and the piece being attacked.
This type of blocking will only work if the attacking piece is a type that can move linearly an indefinite number of squares such as a queen, rook, or bishop and there is at least one empty square in the line between the attacking and attacked piece.
When an opponent's attack on a piece is blocked, the blocking piece is to some extent pinned, either relatively or absolutely, until a future move by either side allows it to be unpinned.
A check on a king by an opponent's queen, rook, or bishop can sometimes be blocked by moving a piece to a square in line in between the opponent's checking piece and the checked king.
This chess tactic can be called interference.