In the mining process, ASICs frantically try to solve complex calculations known as 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 dictates that every 2,016 blocks, the difficulty is modified depending on how many hashes are solved and how many miners there are solving them. This is to keep confirmation times as close to 10 minutes as possible.
If more miners are solving hashes then the difficulty level will increase and vice versa if less miners are solving hashes.
The change in difficulty is also called the “difficulty adjustment”.