I am often asked to explain ground. No, not dirt, but electrical ground.
Counter to what many people might imagine—that ground has something to do with Earth—ground is defined as the lowest point in a circuit.
For example, an aircraft relies upon a solid ground even when flying at 30,000 feet. Your iPhone has a ground despite the fact it's in your pocket.
For our HiFi systems, ground can be the third prong on the mains AC cable or, if you're in Europe or Asia, that ground is built into the sides of the connector
Running on batteries? Ground is the minus of the battery.
To best wrap your head around ground, just think of it as you might the closest electrical point to zero.
Signal ground, power ground. They all tie together at ground zero (forgive the Earth reference).
