1. The short-circuit current is the current through the solar cell when the voltage across the solar cell is zero.
2. The current flowing freely from a photovoltaic cell through an external circuit that has no load or resistance; the maximum current possible.
http://www.pveducation.org/pvcdrom/solar-cell-operation/short-circuit-current (1.); https://definedterm.com/short_circuit_current_isc (2.)