NTP

Network Time Protocol - the set of rules that many computers follow when synchronizing their clock with that of another computer (a Time Server).

NTP is a very complex protocol, requiring approximately 100 pages for its formal definition. A simplified version of NTP, known as SNTP, is used by most ordinary computers. Full NTP is usually reserved for master time-keeping computers, and other computers that need to know the current time with extreme precision (within a few billionths of a second).