Difficulty is a measure of how hard it is to find a valid hash during the Proof of Work mining process. The difficulty adjusts automatically based on the total hash rate of the network to maintain a consistent block time. In Bitcoin, difficulty adjusts every 2,016 blocks (roughly two weeks) to keep the average block time at approximately 10 minutes, regardless of how many miners are active.
Difficulty
Difficulty Explainer Video
What is Mining Difficulty? | Crypto Terms Explained