Freedom from risk or danger; safety. Freedom from doubt, anxiety, or fear; confidence. Something that gives or assures safety, as: A group or department of private guards: Call building security if a visitor acts suspicious. Measures adopted by a government to prevent espionage, sabotage, or attack. Measures adopted, as by a business or homeowner, to prevent a crime such as burglary or assault: Security was lax at the firm's smaller plant. Measures adopted to prevent escape: Security in the prison is very tight. Something deposited or given as assurance of the fulfillment of an obligation; a pledge. One who undertakes to fulfill the obligation of another; a surety. A document indicating ownership or creditorship; a stock certificate or bond.