In computing, a byte is a unit of data that is eight binary (bits) digits long. Thus it has 28 = 256 different values that can be logically mapped to represent letters, numbers or symbols (for example, "a", "7", or "@"). The word was coined by Dr. Werner Buchholz of IBM in 1956.
A byte is abbreviated with a "B". Computer storage space is usually measured in byte multiples, for example 100MB is equal to 100 million bytes - or megabytes - of data.
Other common abbreviations include:
kB = kilobyte = 1024 bytes
GB = gigabyte = 1 billion bytes (although this is an approximation) 
TB = terabyte = 1024 billion bytes (or 1024 GB)
PB = petabyte = 1024 TB
EB = exabyte = one billion gigabytes
Half a byte is referred to as a nibble.