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Great job! So inspiring!
Grove is a 4-wire format used by Seeedstudio for their sensors. They make a bunch of different i/o devices that conform to this standard (leds, speakers, buttons, hall effect sensors, lcds, etc) and they plug into shields that they make for different micro-controllers. It makes it very easy to experiment with different sensors, as all you need to do is plug them into the shield vs wiring up resistors/capacitors etc on a breadboard. I have the Arduino Grove sensor shield and it's very useful for prototyping things.