A byte is a series of bits, usually eight in number, used in computers to represent a character. Byte is a contraction of the words "by eight". Half a byte is sometimes called a "nibble". Originally, computers used 8-bit bytes but gradually this has increased to 16-, 32-, and 64-bit bytes.
A kilobyte is approximately one thousand bytes. Because computers use a binary number system, a kilobyte is precisely 210 or 1,024 bytes.
A megabyte is approximately one million bits. It is precisely 220 bits, or 1,048,576 bits.
A gigabyte is approximately one billion bytes. It is precisely 230 or 1,073,741,824 bytes.
A terabyte is approximately one trillion bytes. It is precisely 240 or 1,099,511,627,776 bytes.