FIR means a complaint of a crime committed. It is also known as First Information Registration.
This is the basic document on basis of which investigation starts.
In every police station a Crime Register is maintained. Such FIR are registered and a number is given.
But suppose a crime has been committed in Ghaziabad and complaint is given in a Delhi Police Station.
Then, Delhi police have to register this complaint as ZERO NUMBER FIR and then it will have to forward it to concerned police station of Ghaziabad which may have power to investigate it. There, a new number will be given to FIR and investigation will start.
In same way, a crime may have happened in Calcutta and complaint can be given in a Mumbai Police Station. Then Mumbai Police Station will register it as ZERO NUMBER FIR and will forward it to Calcutta Police Station for investigation.
Haresh Raichura
5/8/13