FIR stands for First Information Report. The police have to file a FIR whenever a person gives information about a known offence. This information can be given to the police either orally or in writing. A FIR is necessary for the police to begin their investigations into a crime.
The FIR should mention the date, time and place of the offence, details about the offence, including a description of the events. The FIR should also state the name and address of the complainant. There is a prescribed form in which the police register an FIR and it is signed by the complainant. The complainant also has a legal right to get a free copy of the FIR from the police.