It has to do with SI units, marketing, computer science, and a few other intersections. Before marketing took over the term, kilo-, mega-, giga-, and all other methods of measuring data were powers of 2, because binary is a base 2 number system. So a kilobyte is 2^10^ bytes, megabytes are 2^20^ bytes, gigabytes are 2^30^ bytes, etc. These units are denoted as KB, MB, GB, etc.

Well, to marketing ghouls, this standard is just simply too inconvenient because it’s not in base 10. So they simply just rounded up. In small amounts of data, rounding to 1 kilobyte from 1000 bytes isn’t all that far off. But as you can imagine, this skews the correct amount of data as it starts growing to larger units.

Manufacturers were unwilling to listen to the people that understand computers, so IEEE created a new standard unit, the -ibibyte, to clear the confusion that capitalists needlessly invented. So now the units that are in powers of 2 are called kibibytes, mebibytes, gibibytes, etc. these units are denoted with KiB, MiB, GiB, etc.