Internal Program Version: systemd-timesyncd 3.2.3

NTP is the Network Time Protocol

systemd-timesyncd is a system service that may be used to synchronize
the local system clock with a remote Network Time Protocol (NTP) server. 
It also saves the local time to disk every time the clock has been 
synchronized and uses this to possibly advance the system realtime
clock on subsequent reboots to ensure it (roughly) monotonically advances 
even if the system lacks a battery-buffered RTC chip.

https://www.freedesktop.org/wiki/Software/systemd