A unit of computer memory or data storage capacity equal to 1,048,576 bytes (1,024 kilobytes or 220 bytes).
One million bytes.
Our Living Language: In computer science and industry usage, the prefix mega- often does not have its standard scientific meaning of 1,000,000, but refers instead to the power of two closest to 1,000,000, which is 220, or 1,048,576. The calculation of data storage capacity (measured in bytes) is based on powers of two because of the binary nature of bits (1 byte is 8, or 23, bits). Thus, a megabyte is 1,048,576 bytes, although it is also used less technically to refer to a million bytes. Other numerical prefixes are interpreted similarly. With data transmission rates (measured in bits per second), a bit is considered as a signal pulse, and calculations are generally based on powers of ten. Thus, a rate of one megabit per second is equal to one million bits per second. However, in certain technical contexts, megabit can also refer to 1,048,576 bits. Similarly, the prefix kilo- refers to 1,000 or 210 (1,024); giga- to 1,000,000,000 (one billion) or 230 (1,073,741,824); and tera- to 1,000,000,000,000 (one trillion) or 240 (1,099,511,627,776).