Bitcoin mining is the process by which new bitcoins are created and transactions are sent across the network. Both the people who engage in it and the devices that are used for mining are called "miners". In the process of mining, the miners' computers perform the so-called "hashing", producing proof-of-work - they take a series of randomly generated input data strings and apply a specific cryptographic function to it (SHA-256 in Bitcoin's case). The result of each calculation will always be the same "hash", unique to any particular input, but its exact value cannot be predicted until the actual calculation is performed. The network has an overall "target" value, and as soon as any miner gets a hash which is equal to or lower than the target, they get to register all the transactions which took place on the network since the last "hit", package them into a block, add it to the end of the Blockchain, and credit a specific amount of bitcoins to their own account (these bitcoins are created "out of nothing" to reward the miner for the time and electricity they spent on cracking hashes). Initially, any person could use their PC to download a Bitcoin client and start mining bitcoins. They still can, but by now it is economically infeasible, as the mining industry is dominated by ASICs - highly efficient machines developed specifically for the purpose of mining Bitcoin.