megabyte
Strictly speaking, a megabyte is 1,048,576 bytes. For example, a 20 megabyte hard drive, besides being an antique, would hold 20,971,520 bytes, rather than 20,000,000 bytes.
However, the term can also mean 1,000,000 (one million) bytes when dealing with throughput or transfer rates, such as '5 megabytes per second,' which means 5 million bytes per second.