A more thorough explanation:

The Federal Bureau of Prisons (BOP) is a law enforcement agency that manages incarcerated individuals. It is part of the Department of Justice and is led by a Director who reports to the U.S. Attorney General. The BOP's main goal is to protect public safety by ensuring that federal offenders serve their sentences in facilities that are safe, humane, cost-efficient, and secure. The BOP also provides reentry programming to help inmates successfully return to their communities.

The BOP has several duties, including managing and regulating federal penal and correctional institutions, providing suitable quarters for all inmates, providing for the protection, instruction, and discipline of all inmates, and providing technical assistance to state, tribal, and local governments in improving their correctional systems. The BOP also establishes prerelease and reentry planning procedures.

For example, the BOP has custody over approximately 150,000 inmates, with about 85% of them confined in BOP-operated facilities. This means that the BOP is responsible for ensuring that these inmates are housed in safe and secure facilities and that they receive the necessary care and support to successfully reintegrate into society after their release.