What Is the Difference between Difficulty and the Target Hash?

The difficulty is a human-readable, relative number that expresses how much harder it is to mine a block compared to the easiest possible block. The target hash is the actual 256-bit number that a valid block header hash must be less than or equal to.

The difficulty is derived from the target hash. When the network adjusts difficulty, it is actually adjusting the target hash value, which in turn changes the difficulty number.