Question

what is the difference between advancing monsoon and retreating monsoon?

Answer 1

advancing monsoon is one which comes toward india
retreating monsoon is which goes from where it has come

advancing monsoon is due to the low pressure
retreating monsoon is due to the high pressure

Answer 2

Advancing monsoon - 
Coming of monsoon
Due to low pressure
Showers firstly on Kerela
Starts in June

Retreating monsoon -
Going of monsoon
Due to high pressure
Showers on Island
Ends in September

Hope it Helps!! ^_^