I - current in Amps. The I comes from the archaic term intensity.

Imp current at the panel's maximum power output (see Vmp)

Isc - Amps when short circuited; this is when your solar panels are connected only to themselves. This is the highest current your panels can theoretically produce.

Pmax maximum power a panel will make. Vmp * Imp = Pmax

Setpoint - a value used to place a limit or border on a particular operation. If your refrigerator is set hold 40F temperatures then 40F is the setpoint. If your charger floats at 13.2v then 13.2v is the Vfloat setpoint. Setpoints may be preset by the manufacturer or configured by the user.

V - Volts

Vabs - charge controller voltage setpoint for Absorption stage

Vbatt - actual voltage of the battery bank.

Vfloat - charge controller voltage setpoint for Float stage

Vmp - voltage at which a panel makes maxiumum power (watts)

Voc - volts in open circuit; when your solar panels are not connected to anything. This is the highest voltage your panels can theoretically produce.

Vpanel - voltage the controller is running the panel[s] at

W - power in Watts