MHz or MegaHertz stands for "One Million" clock cycles per second. This unit is used to measure the maximum frequency or "change of state" of the rocker switch for electronics. Frequency is the upper limit of performance because data change or calculations involve a state change.

GigaHertz (GHz) is One Billion cycles or 1000 MegaHertz (MHz).

Since hertz is used to measure frequencies, it also applies to radio frequency. But this has nothing to do with computational performance.

Frequency in MHz is used as a measure for chips (CPU, GPUs) and memory (RAM, VRAM), as well as for buses (data transport lanes).

Frequency describes the rhythm of events when they occur. The higher the rhythm, the stronger the change and calculations.