Synchronous
From Computer History Wiki
Synchronous is a term which means that some event, or device, operates on a clock, or with fixed timing.
Thus, elements in a synchronous logic system respond to an external control which imposes synchronizing timing; an external signal is used to control when everything changes. A clock signal is used to control when flip-flops store their inputs, for example.
A synchronous serial line uses a fixed clock (which is usually provided by one end, or by the transmission channel itself) which is carried on a separate signal line.
Contemporary logic design is usually synchronous; but older logic systems were often asynchronous, without use of a clock.
