Final answer:
The FBI, which stands for the Federal Bureau of Investigation, is the chief federal law enforcement agency within the United States.
Step-by-step explanation:
The acronym 'FBI' stands for the Federal Bureau of Investigation. It is the chief federal law enforcement agency within the United States. The FBI's activities are focused on investigating federal crimes, protecting the country against terrorist threats, and upholding the rule of law. Unlike the CIA which operates mainly overseas, the FBI's jurisdiction is limited to the U.S. national borders.