It means electrical ground, or earth ground. Referring to the electrical path back to the battery ground, or - side of battery.

no it cannot

Connect a slave battery to the alternator live terminal and an earth. Then the central locking should work.

If one terminal of a battery is earthed (and, by this, we normally mean a 'chassis earth'), then an earth fault within the circuit supplied by the opposite terminal will result in the battery being discharged. The rate of discharge depends on the resistance of the earth fault.

A partial earth