Animation

GND at node C: that node is taken as 0 V · V(A) = +9.0 V, V(B) = +4.5 V, V(C) = 0.0 V · the differences stay the same: A − B = 4.5 V, B − C = 4.5 V · I = 9 V / 2 kΩ = 4.5 mA does not change · GND produces no voltage, it is only the 0 V reference

One node is chosen as 0 V, and the voltages of the other nodes are expressed relative to it. The GND symbol does not produce voltage and does not create a protective earth by itself.
No physical dimension; a schematic symbol or a connection point on the board

Tools

Ground / GND (reference point)

In simple terms

What is this?

The ground-floor mark of the circuit. Just as you always measure height from the floor, you always measure voltage relative to this.

What is it for?

Gives voltages a common starting point; it shows where to put the black probe of a multimeter.

Where do you see it?

Every device has it on its board as the common negative line; the negative wire of a USB cable is one too.

How do you spot it?

Not a real part, but a symbol: horizontal lines getting shorter and shorter on the schematic, the point labelled GND on the board.

Caution:

Not every GND is connected to the earth; don't join the ground lines of separate circuits without knowing.

Technical definition

GND is the name of the reference node taken as zero volts in the circuit; it is not a part that consumes energy. Every voltage is a difference between two points, so a reference is needed when you state a node voltage. Signal ground, the metal chassis connection and protective ground (PE) are not the same thing; they are joined only if the design requires it.

ReferenceSelected node 0 V

Terminal count1 connection point

MeasurementThe voltage difference between two points

Schematic symbol Same in IEC and ANSI

IEC 60617: the drawing style used in Türkiye and Europe.

Pins 1

1GND referenceThe node taken as 0 V in the circuit; the reference for the black probeGND

Features typical

Reference: Selected node 0 V
Measurement: V = Vmeasured − Vreference
Signal ground: Common reference and return path of the signal
Chassis ground: Metal case connection; may be separate from signal GND
Protective ground (PE): Electrical safety conductor; not a synonym for GND
Floating circuit: Its reference does not have to be tied to mains ground
Example part: 0 V reference node in the schematic

Common mistakes

Assuming every GND is tied to groundThe GND of a battery-powered circuit usually floats. The symbol alone does not mean a protective ground connection.

Stating a voltage without a referenceWhen you call a point 5 V, say which node it is relative to; the multimeter measures the difference between two probes.

Joining isolated circuitsJoining the GND of two separate circuits can remove isolation. Separate the chassis, PE and signal return on purpose.

Where it is used

Defining the schematic referenceMultimeter black probe pointExamining the common signal return

Try it in the Lab