Mega-

Mega is a unit prefix in metric systems of units denoting a factor of one million. It has the unit symbol M. It was confirmed for use in the International System of Units in 1960. Mega comes from.

Common examples of usage

Megapixel: 1 million pixels in a digital camera
One megatonne of TNT equivalent amounts to approx. 4 petajoules and is the approximate energy released on igniting one million tonnes of TNT. The unit is often used in measuring the explosive power of nuclear weapons.
Megahertz: frequency of electromagnetic radiation for radio and television broadcasting, GSM, etc. 1 MHz = 1,000,000 Hz.
Megabyte: unit of information equal to one million bytes.
Megawatt: equal to one million watts of power. It is commonly used to measure the output of power plants, as well as the power consumption of electric locomotives, data centers, and other entities that heavily consume electricity.
Megadeath: is one million human deaths, usually used in reference to projected number of deaths from a nuclear explosion. The term was used by scientists and thinkers who strategized likely outcomes of all-out nuclear warfare.

Exponentiation

When units occur in exponentiation, such as in square and cubic forms, any multiples-prefix is considered part of the unit, and thus included in the exponentiation.

1 Mm² means one square megametre or the size of a square of by or, and not .
1 Mm³ means one cubic megametre or the size of a cube of by by or 10¹⁸ m³, and not

Computing

In some fields of computing, mega may sometimes denote information units, for example, a megabyte, a megaword, but denotes units of other quantities, for example, transfer rates: =.
In the case of 3½-inch floppy disks, sizes were given in megabytes of 1000KB or bytes.
The prefix mebi- has been suggested as a prefix for 2²⁰ to avoid ambiguity.