Mega is a prefix that is used as a multiplier. The prefix mega is written as a uppercase "M" in front of the measure.
In the "analog" world Mega represents the numeric value of 1,000,000 (a million or 106); such as a frequency of 90 MHz, which is 90,000,000 Hz.
When used in the digital world, Mega represents the numeric value 1,048,576 (1024×1024 or 220; e.g. a bit rate of 8 Mbit/s, which is a rate of 8,388,608 bits per second).