Ground & reference

Ground (GND) is a chosen 0 V reference node. Many circuits also use it as a return path, but not every current must flow through ground. A voltage may be measured between any two nodes; node voltages are usually stated relative to the chosen reference.

Because voltage is always a difference, you need a fixed reference to measure against — and ground is it. Pick a different reference point and every voltage in your circuit changes by the same offset, even though nothing physical changed. Choosing a common ground keeps everyone’s numbers consistent.

Ordinary low-voltage boards exchanging single-ended signals usually need a common ground so both interpret voltages against the same reference. Isolated interfaces deliberately work without joining their grounds. Follow the interface and power-supply design rather than assuming every ground must be connected.