A Byte is a measurement of the size of data. A Kilobyte (KB) is equal to 1000 bytes (measurement for a unit of data). A Megabyte (MB, Meg) is equal to 1000 Kilobytes. A Gigabyte (GB) is equal to 1000 Megabytes. Bytes can be most easily understood in terms of data storage on your hard drive for example.
This is not to be confused with a Bit which is eight times smaller than a Byte. Broadband speeds are measured in Bits per second. A Kilobit (KBit) is equal to 1000 bits . A Megabit (MBit) is equal to 1000 Kilobits. A Gigabit (GBit) is equal to 1000 Megabits.