“Difficulty” is a term related to Bitcoin mining and basically describes how difficult it is to produce a new block.
In the mining process, ASICs frantically try to solve complex calculations called hashes every 10 minutes in order to secure the next batch of transactions. By processing transactions in this way, miners are rewarded with Bitcoin.
Bitcoin’s protocol states that every 2,016 blocks, the difficulty is changed based on the number of hashes solved and the number of miners solving them. This is to keep confirmation times as close to 10 minutes as possible.
If more miners are solving hashes, the difficulty level will increase and vice versa if fewer miners are solving hashes.
Changing the difficulty is also called “difficulty adjustment”.