A First Information Report (FIR) is a written document prepared by law enforcement upon reporting a crime, serving to officially inform the police and initiate investigations, with its legal basis found in section 154 of the Indian Penal Code. It includes essential details such as the complainant's information, crime specifics, accused information, and witness accounts, acting as a crucial legal record and evidence in court. FIRs play a significant role in criminal investigations, as they guide police action and can be used to corroborate testimonies, with discrepancies potentially undermining witness credibility.