In general this term is used to describe things that are somehow coordinated in time. In signal transfer it usually means that multiple devices are synchronized to the same clock, which typically means information can move from one to the other without extra layers of handshaking and confirmation. For example, a S/PDIF transfer of digital audio data is a synchronous transfer, i.e. it happens at the rate of a synchronized clock signal (at the sample rate). It is more or less “assumed” that the information arrived in tact, though some systems still employ various types of confirmation protocols. In fact, in some contexts, contrary to the above, synchronous data transfer requires that each communication respond in turn before initiating a new communication, which keeps them synchronized.