1. Network Time Protocol - protocol built on top of TCP/IP that assures accurate local timekeeping with reference to radio, atomic or other clocks located on the Internet. This protocol is capable of synchronizing distributed clocks within milliseconds over long time periods. From Linux Guide @FirstLinux

2. Daemon and utilities for full NTP v4 timekeeping participation. The Network Time Protocol allows for the synchronization of clocks on networked computers. The ntpd daemon implements NTP, allowing Unix systems to participate in this synchronization. To minimize resource consumption in the general case, this package no longer includes the actual daemon. You will need either ntp-simple or ntp-refclock, depending on whether you want the drivers for radio clocks included in the refclock version of the daemon. NTP was designed with attention to details which might introduce systematic bias into the computations, and the protocol is capable of synchronizing with even the most precise external time sources. For more information on how NTP works, and how to configure a campus of ntpd daemons, load the optional Debian package 'ntp-doc'. From Debian 3.0r0 APT

3. The Network Time Protocol (NTP) is used to synchronize a computer'stime with another reference time source. The ntp package contains utilities and daemons that will synchronize your computer's time to Coordinated Universal Time (UTC) via the NTP protocol and NTP servers. The ntp package includes ntpdate (a program for retrieving the date and time from remote machines via a network) and ntpd (a daemon which continuously adjusts system time). Install the ntp package if you need tools for keeping your system's time synchronized via the NTP protocol. From Redhat 8.0 RPM