Bitcoin mining difficulty is a measure of how difficult it is to mine a Bitcoin block, or in other words, how much computing power is required to solve the mathematical problem that is necessary to mine a Bitcoin block.
Mining difficulty is adjusted over time to ensure that on average, miners will find a new block at the same rate, regardless of the total amount of computing power being used to mine. This is necessary in order for the Bitcoin network to remain secure and for miners to be able to receive rewards for their work.
The Bitcoin network adjusts the mining difficulty every 2016 blocks, or approximately every two weeks. The difficulty is adjusted based on the total amount of computing power that is used to mine on the network. If the total network hash rate increases, the difficulty will increase in order to maintain the same average block time. Similarly, if the total network hash rate decreases, the difficulty will decrease in order to maintain the same average block time.
The current mining difficulty is an important factor to consider when deciding whether or not to mine Bitcoin. As the difficulty increases, it becomes more difficult to mine a new block, and therefore less profitable. Conversely, as the difficulty decreases, it becomes easier to mine a new block and more profitable.