Synchronization (alternating current)
In an alternating current (AC) electric power system, synchronization is the process of matching the frequency, phase and voltage of a generator or other source to an electrical grid in order to transfer power. If two unconnected segments of a grid are to be connected to each other, they cannot safely exchange AC power until they are synchronized.
Source: Wikipedia — Synchronization (alternating current) (CC BY-SA 4.0)