Wiktionary
n. (context computing English) Strictly, 230 (1,073,741,824) bytes, as opposed to a gigabyte.
Wikipedia
The gibibyte is a multiple of the unit byte for digital information. The binary prefix gibi means 2, therefore one gibibyte is equal to = 1024 mebibytes. The unit symbol for the gibibyte is GiB. It is a member of the set of units with binary prefixes defined by the International Electrotechnical Commission (IEC).
The gibibyte is very closely related to the gigabyte (GB). The GB is defined by the IEC as 10 bytes = , ≈ . 1024 gibibytes are equal to one tebibyte. In the context of computer memory, Gigabyte and GB are customarily used to mean 1024 (2) bytes, although not in the context of data transmission and not necessarily in the context of hard drive size. The word gibibyte was coined in 1998.
Binary prefixes are increasingly used in technical literature and open source software, and are a component of the International System of Quantities.