A mebibyte (MiB) is a unit of data storage equal to 220 bytes, or 1,048,576 bytes. Like kibibyte (KiB) and gibibyte (GiB), mebibyte has a binary prefix to remove any ambiguity when compared to the multiple possible definitions of a megabyte.
Due to historical naming conventions in the computer industry, which used decimal (base 10) prefixes for binary (base 2) measurements, the common definition of a megabyte could mean different numbers depending on what was measured — memory in binary values and storage space in decimal values. Using mebibyte to refer specifically to binary measurements helps to address the confusion.
NOTE: Windows operating systems calculate storage and file sizes using mebibytes (MiB) and gibibytes (GiB), but use the labels for megabytes (MB) and gigabytes (GB). MacOS uses actual megabytes and gigabytes when calculating sizes. The same disk or file will show slightly different values in each operating system — for example, a file that is exactly 1,000,000 bytes will appear as 976.56 KB in Windows and 1 MB in MacOS.