(MB, colloquially "meg") A Unit of data equal to one million bytes but see binary prefix for other definitions. A megabyte is 1000^2 bytes or 1000 kilobytes.
The text of a six hundred page paperback book stored as ASCII characters contains about one megabyte of data. The complete King James bible is 5.2 megabytes.
1000 megabytes are one gigabyte.