A sequence of events is isochronous if the events occur regularly, or at equal time intervals. Isochronous timing differs from synchronous timing, in that the latter refers to relative timing between two or more sequences of events. The term isochronous is used in different technical contexts, but often refers to the primary subject maintaining a certain interval, despite variations in other measurable factors in the same system.
In horology, a mechanical clock or watch is isochronous if it runs at the same rate regardless of changes in its drive force, so it keeps correct time as the mainspring unwinds. This includes clocks that use a pendulum.
In telecommunications, an isochronous signal is one where the time interval separating any two corresponding transitions is equal to the unit interval or to a multiple of the unit interval; but phase is arbitrary and potentially varying.
The term is also used in data transmission to describe cases in which corresponding significant instants of two or more sequential signals have a constant phase relationship.