arbitrary word-forming element meaning "billion" in the metric system, 1947, from Greek gigas "giant" (see giant).
giga- pref. One billion (109): gigahertz.
A prefix that means:
One billion (109), as in gigahertz, one billion hertz.
230 (that is, 1,073,741,824), which is the power of 2 closest to a billion, as in gigabyte.