The hash is a mathematical application that is used to calculate the mining capabilities of given hardware. This includes the use of powerful computers backed by special software to mine cryptocurrencies.
Megahashes per second (MH/s) is the measuring unit used to calculate the computational power of these systems. One megahash is equivalent to one million hashes. The sole purpose of these mining rigs is to solve the cryptographic function for the current block.
With the ever-increasing difficulties, it has become next to impossible to mine with hashes per second speed. This is where kilohash (KH/s) and megahash (MH/s) are being implemented on systems. Based on the hardware in use, these hash rates can drastically change as well.