(1) See
synchronous and
synchronous transmission.
(2) Ensuring that the same photo, video or document is in two or more devices all the time. See
data synchronization.
(3) Keeping time-of-day clocks in two devices set to the same time. See
NTP.
(4) Keeping the clocks of two devices beating at the same rate. See
synchronous transmission.
(5) Sending identical electronic signals from two transmitters. See
MediaFLO.