Pilot function is one wire communication between EV and EVSE (Charger). It is basically a PWM generated from EVSE according to the current capability of the charger and send to the EV. So, EV must drawn that amount of current from the EVSE.
Pilot function make sure the power deliver only when the connection established between EV and EVSE otherwise not.
In AC slow and fast charging, all the function done by means of pilot wire.
You can read whole AC charging related standard given by ARAI in following link.