Accuracy and stability
1PPS
Also: pulse per second, PPS
A 1PPS signal is a short pulse whose rising edge coincides exactly with the start of every UTC second. GNSS receivers provide 1PPS; master clocks and measurement equipment use it to discipline or compare their internal time.
The signal itself carries no date or time, only the exact moment of the second boundary. That is why it is often combined with an NMEA time sentence that provides the date and time.