Where is the Ground in a Simple Electronic Circuit
"Ground" is a much abused term in electricity and electronics.  Occasionally, particularly in AC power distribution and some radio antenna systems, it does mean "a connection to the earth".

However, in most electronics, particularly portable battery-operated devices, "ground" is just the point in the circuit that the designer chose to call "zero volts" and to use as a reference when measuring voltages elsewhere in the circuit.  I think it would be better to call it "reference" or "common", but we seem to be stuck with misusing "ground".

In most circuits these days, "ground/reference" is the most negative terminal of the power supply, so voltages elsewhere are positive relative to "ground".

In some cases, the positive terminal of the power supply is "ground", and voltages elsewhere are therefore negative (there's one logic family that is supposed to run from a -5.2 volt suppply).

In many analog circuits, particularly those using op-amps, "ground" is the middle of the power supply, so we have both negative and positive voltages in the circuit.