Ground (or Earth or chassis ground) in an electronics context generally means the reference point or potential, where signals or voltage readings are referenced to. Also usually where any screening or metalwork connects to.
In most modern single-supply devices, power negative is considered 0V and also "ground" or "chassis".
(In early or transistor circuits & occasionally now still, the positive supply is 0V and all voltages are measured negative of that).
With dual-supply devices like some audio amps and opamps etc., that have eg. +15, 0V and -15 power connections, the 0V is normally considered ground.