Beware of the word "ground," since it has several conflicting definitions. The experts may be able to figure it out from syntax, but for everyone else, we can avoid much confusion by avoiding the word "ground." Use less general terms instead.
For example, "ground" can mean one or more of the following, or even a mixture of several:
"Ground" can be a common connection for multiple power supplies, but not connected to the earth. The chassis of a car is one example, and while most manufacturers connect their chassis to the battery negative terminal, older Volkswagens connected theirs to the battery positive. "Ground loops" refer to this definition.
"Ground" can mean an arbitrary reference point in a circuit, "schematic ground" or a point used to define the voltage-drops throughout the device.
"Ground" can mean the inside of a shielded enclosure, including any shield-planes built into a pc board. In many amplifiers, the metal box is the system ground. In high speed circuitry we'll find separate "logic ground" and "analog ground," each connected to separate conductors used as shields.
"Ground" can mean an RF counterpoise: a connection to a large conductive object. In portable receiver front ends, a short wire is one "antenna" terminal, while the other terminal connects to the rest of the circuit as a "ground."
"Ground" can mean "the opposite of electrically floating."
"Ground" can mean "Earth connection," a terminal with an actual metal stake pounded into the dirt. Earth connections are important with lightning hazards and AC line safety, with AM and shortwave antennas, PA sound systems in wet outdoor environments, high-voltage electrostatic build up and ESD/EMP problems.