MHz

MHz means millions of cycles per second frequency. 

To understand MHz, we might first need to understand how AC voltage works and also what the term frequency means.  AC voltage implies that a signal is not always a constant voltage - but that it is sometimes high relative to another potential, and then will fall and be a similar value, and then will fall even more in voltage and now be a negative voltage, and then climb back more positive to zero voltage and then to the original high voltage.  Such a voltage is called AC - for Alternating Current.  Wireless signals are a form of AC since their voltage (amplitude) varies just as AC does.

Since the voltage or amplitude varies over time, we can now talk about frequency.  Frequency is the number of times (cycles) per second that the voltage goes negative and then returns back to its original value.  We call this frequency, or we can also call it the number of cycles per second, or we can also refer to it as a number of Hertz.  Hertz is really just a new name for cycles per second.  MHz then refers to millions of cycles per second or millions of Hertz.  If we talk about 900 MHz what we are really saying is that the wireless signal amplitude (voltage) varies from its high point to its low point 900,000,000 times per second.  So, we would say that we are talking about a frequency of 900 MHz (Megahertz).