Definition from Nolo’s Plain-English Law Dictionary
Formerly referred to as the Border Patrol, this is now an agency within the Department of Homeland Security (DHS). One of its responsibilities is to keep the U.S. borders secure from people crossing illegally. Another one is to meet travelers and returning residents arriving at U.S. airports and border posts, and to check their visas or other admission documents in order to decide whether they should be allowed into the United States. If not, CBP has the power to order them to return home immediately.