Kibibyte (KiB)

In 1998, the IEC decreed to call 1,024 bytes a kibibyte — a term which is only slowly catching on. During the transition period, the IEEE suggests using a lower-case "k" for the decimal kilo (1,000) and, if properly pointed out, an upper-case "K" for the binary kilo (1,024), thereby taking the historical development into account. This is versus the kilobyte, where kilo is commonly defined as 1000.

It should be noted that many reject the IEC's binary prefixes (kibi-, mebi-, gibi-, tebi-, pebi-, exbi-) on the basis that they sound really, really dumb.