Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Earth ground: It's just what it sounds like. The electrical potential of the Earth. Pound a metal stake in the ground and it will be your terminal for Earth ground.
Chassis ground: The electrical potential of the frame or box that contains a device. Obviously it will be made of a conductive material. For a computer, it would be the case.
Signal ground: This one's a little trickier. It's an arbitrarily chosen (by the circuit designer) point in any given circuit assumed to have zero electrical potential (0 volts). It's useful for making measurements in a circuit.
The black lead of a power supply is typically the ground lead. In a schematic it's designated by the symbol that looks like an inverted "christmas tree".