What is the difference between Serial and Parallel transmission of data?

Serial transmission is where bits are transmitted one at a time over a single channel, particularly used within USB devices. Parallel transmission is where bits are sent simultaneously over their own individual channel. For example, if we were dealing with 8 bit integers, each of the 8 bits in the integer would all be send at once over their own unique channel. This is generally only used for internal computer components since it is limited to very short distances, due to the potential for interference.