Answer:
megabyte (note correct spelling) = 106 bytes = 1,000,000 bytes
mebibyte = 220 bytes = 1,048,576 bytes
Historically megabyte has been used to mean both values (and others, such as 1,1024,000).
Mebibyte is unambiguously the binary-based value, but it is not widely used and megabyte continues to be used to for both meanings.