Definition
The target is the threshold that determines whether a block hash is valid. When miners hash a block header, the resulting 256-bit number must be numerically less than the current target. Since hash outputs are effectively random, a lower target means fewer possible valid hashes, requiring more attempts on average.
The target is encoded in the block header’s ‘bits’ field using a compact format. It is recalculated every 2,016 blocks based on how long the previous 2,016 blocks took to mine. The relationship between target and difficulty is inverse: difficulty = max_target / current_target.
In Simple Terms
The threshold a block hash must be below to be valid. Lower target means harder mining.
A 256-bit number that a block's hash must be below for the block to be considered valid. A lower target means higher difficulty.