A gibibit is a measurement of binary data. It is similar to a gigabit, which is a thousand million bits (a billion bits in the US, but 'billion' is different in the UK!), which can be written 109. A gibibit is slightly more than a gigabit, however. A gibibit is exactly 230 bits. Powers of 2 have always been the usual measurement of binary data because it's much easier for computers to do arithmetic and move data around when the numbers are powers of 2. (0, 1, 2, 4, 8, 16, ...)
| Unit | Gibibit | Gigabit |
|---|---|---|
| Definition | 1 073 741 824 bits | 1 000 000 000 bits |
| Abbreviation | Gib | Gb |
For more information, you can read the NIST's binary prefixes page or read the Wikipedia entry on Binary Prefixes.