The gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means $10^9$ in the International System of Units (SI), therefore 1 gigabyte is $1,000,000,000 \; bytes$. The unit symbol for the gigabyte is $GB$ or $Gbyte$, but not $Gb$ (lower case b) which is typically used for the gigabit. Historically, the term has also been used in some fields of computer science and information technology to denote the $gibibyte$, or $1073741824 \; bytes$.
Gigabyte