In units of measurement, a factor of one thousand million or 109. In computing, often a factor of 230 (1,073,741,824).
[Greek gigas, giant.]
This is one of the standard SI (Système International) decimal prefixes (see the entry Words for multiples), which appears in such compounds as gigahertz and gigawatt. Computer science has borrowed the unit—as it has with others—to refer to powers of 2 rather than 10, so that a gigabyte, for example, is usually taken to be 230 bytes. This is true also of other computer terms such as gigabit or gigaflops (strictly 230 floating-point operations per second).