BFR Imprinting is the process by which a soldier acquires BFR certification.
The imprint is used to tune the Resonance Crystals implanted in all soldier to the thought-patterns of that particular soldier so as to allow the soldier to control the systems of a BFR.
The process includes achieving 5 Cavern Captures and getting 75 unique kills inside the caverns. Kills on enemies in vehicles or Ancient Sentry Turrets do not count toward the kill requirement. After the capture and kill requirements, you must step into the core beam at the Core Complex in one of the caves to complete the imprinting process. Characters created before June 18, 2009 are automatically imprinted and do not have to go through this process (see: 6th Anniversary Update).