Comprehensive Strategy for Overstay Enforcement and Deterrence (Fiscal Year 2017 Report to Congress) [open pdf - 1MB]
From the Executive Summary: "This report outlines DHS's comprehensive strategy for overstay enforcement and deterrence, to include information on existing operations and planned improvements. Each year, millions of nonimmigrants are admitted lawfully to the United States for an authorized period of time. The authorized period can be a fixed period, or can be based on completion of a certain activity, such as a student seeking a college degree or technical/practical training. A nonimmigrant becomes an 'overstay' when he or she remains in the United States beyond his or her authorized period of admission."
U.S. Department of Homeland Security: https://www.dhs.gov/