The Grove-Relay is a digital normally open switch that controls a relay capable of switching much higher voltages and currents than your normal microcontroller boards. When set to HIGH, the LED will light up and the relay will close allowing current to flow. The relay peak voltage capability is 250VAC/30VDC at 5 amps.
This module V1.2 is suitable for 3.3V and 5V.
A Grove cable is included.
More information is available on the website of Seeed Studio and wiki.