The mental energy and effort required for mining blocks on a network.
Difficulty in the world of cryptos refers to the degree of effort that users need to exert before they can mine blocks on a network and earn rewards. The level of this difficulty is generally determined by the network consensus in the form of established rules. Without these rules and imposed complexity in the mining process, the computational processes needed to mine blocks will be too simple. As a consequence, the required hashes would no longer be rarely computed and the entire mining process would be rendered ineffective.
The level of difficulty in the mining process is one of the indicators of a blockchain’s security. The harder the difficulty, the more secure and stable the network.