What is a Gigabyte?

Gigabyte, $GB$, is a unit of digital information. Giga is used as a unit prefix in metrics system. It represent a numerical value $10^9$ or $1,000,000,000$. List of SI prefix can be found on Wikipidia.

There are two common ways unit of information is represented. One is in decimal (base 10) form and the other is in power of 2 (binary). $Gigabyte$ is referring to the base 10 format, unlike $Gigibyte$ which is referring to base 2 format.

$$1\,Gigabyte => 1\, GB\,(shorthand form)$$

$$1\,GB = 1,000,000,000\,byte = 10^9 bytes$$

More examples can be found on Stanford's Kilobytes Megabytes Gigabytes Terabytes article

What is a Byte?

Byte is used to measure unit of digital information. In general, byte is equivalent to 8 bits in computers. the symbol for byte is $B$ (capital b) as Specified in IEC, IEEE and Metric Interchange Format.

For more info take a look at Bits and Bytes definition from Stanford

$$1\,B = 8\,bites$$