Grove – MOSFET enables you to control high voltage and high current. MOSFET is a kind of switch, but its switching frequency can reach up to 5MHz, much faster than normal mechanical relay. It can for example be used to switch a DC motor or a 24Vdc LED strip on and off.
There are two screw terminals on the board. One for outer power source and the other for device you want to control. Grove – MOSFET will pass the power from one end to another when closed. But if outer power source is absent, your device can still draw power from microcontroller via the Grove interface.
More information is available on the website of Seeed Studio and wiki.