The minimum proof-of-work threshold required to mine a block. A higher number means more Hash Rate is required to find a block in an average time of 10 minutes.
Before the Aug 1, 2017 Bitcoin Cash (BCH) fork, Difficulty was re-calculated every 2016 blocks. Now, Difficulty is re-calculated every block to ensure blocks are found every 10 minutes on average. As more computers attempt to mine Bitcoin Cash (BCH) and increase the Hash Rate, the difficulty will increase. If the Hash Rate decreases, difficulty will decrease.