Network Difficulty is an ever-changing metric in mining, which strongly influences how profitable a particular currency can be mined at a given point in time
Mining difficulty is a measure of how difficult it is to solve the mathematical problem of deciding a block is suitable and receiving a reward for it, i.e., finding the right hash.
The fact is that every cryptocurrency has a block time in its description, and in order to keep it approximately constant, the notion of complexity was introduced. Otherwise, with increased processing power, all coins would be mined very quickly.
