||The examples and perspective in this article may not represent a worldwide view of the subject. (March 2013)|
There are several definitions for the term lockdown, the most common of which pertains to a state of containment or a restriction of progression. A lockdown is an emergency protocol to prevent people or information from escaping, which usually can only be ordered by someone in command. Lockdowns are also used to protect people inside a facility or, for example, a computing system, from a dangerous external event.
There may be various levels of lockdown. For example, in the case of buildings, a partial lockdown means that the doors leading outside of the building are locked and people may not exit or enter the building. A full lockdown means that people must stay where they are and may not exit or enter a classroom, apartment unit, store unit, an office space, condo unit or the building. If people are in a hallway they must go into the nearest classroom, apartment unit, condo unit, office space or store unit.
In its most common usage in corrections units, the term lockdown can be defined as a course of action to control the movement of inmates. Confining all prisoners, except workers, to their cells until the end of the day is a good example of a "lockdown period" in a corrections schedule. However a "full lockdown" is used when all prisoners are locked in their cells to prevent a riot or unrest from spreading or during an emergency.
In US guidelines, occasions for preventing entry into a hospital may include: power failure, earthquake, flooding, fire, bomb threat, hostage crisis and active shooter. Occasions for preventing both entry and exit from a hospital may include: external contamination, civil disturbance and abduction of an infant or child.
The term has risen in use only very recently, see  for a graph of its frequency history.
In December 2005, the New South Wales Police Service initiated a lockdown of the Sutherland Shire and other beach areas of New South Wales to contain race rioting (and retaliative strikes). The New South Wales Labor government, in an emergency sitting of parliament, passed an array of amendments to legislation giving the New South Wales Police Service additional powers to 'lock down' targeted areas and roads within New South Wales. The legislation introduced to deal with the 2005 Cronulla riots was the Law Enforcement Legislation Amendment (Public Safety) Act 2005 (NSW). The Law Enforcement Legislation Amendment (Public Safety) Act 2005 (NSW) amended four separate pieces of legislation:
- Crimes Act 1900 (NSW)
- Bail Act 1978 (NSW)
- Criminal Procedure Act 1986 (NSW)
- Law Enforcement (Powers and Responsibilities) Act 2002 (NSW)
Under their new powers the New South Wales Police Service locked down targeted areas and roads at Cronulla, Bondi, Coogee, Maroubra and Brighton-le-Sands to prevent persons of Middle Eastern appearance from committing reprisal attacks and prevent white supremacist agitators from further violence.
An example of a campus/school lockdown was demonstrated at the University of British Columbia (UBC) on January 30, 2008, when an unknown threat was made and the Royal Canadian Mounted Police (RCMP) issued a lockdown on one of the buildings on campus for six hours, cordoning off the area, and a campus alert was sent via email to everyone affiliated with UBC while students and faculties were to remain locked in the building.
On April 10, 2008, two Canadian secondary schools were locked down due to suspected firearm threats. George S. Henry Academy was locked down in Toronto, Ontario at approximately 2:00 p.m. The Emergency Task Force (TPS) were contacted and the lockdown lasted for more than two hours. New Westminster Secondary School was locked down in New Westminster, British Columbia at approximately 1:40 p.m. The Emergency Response Team (ERT) were called and the school was under lockdown until 4:30 p.m. Due to the size of the school some students were not able to leave until 7:00 p.m.
||The examples and perspective in this article may not represent a worldwide view of the subject. (April 2013)|
Another example of a lockdown would be an air raid emergency. During the 1940s and 1950s, neighborhoods such as Detroit, MI would practice a blackout. During this time, the city's Civil Defense workers would immediately activate the neighborhood air raid siren, and families would be required to do the following in order: 1. Shut off all appliances, such as stoves, ovens, furnaces; 2. Shut off valves for water and natural gas or propane, as well as disconnect electricity; 3. Close blackout curtains (plain black curtains that would block light from coming in or going out). Unlike an atomic bomb, where white curtains are used to reflect the blast, black curtains were used to prevent any airborne enemies from seeing in windows; 4. Get to a public shelter, a bomb or fallout shelter, or the household basement, and stay there until the local police dismissed the blackout. Although no longer practiced air raid drills are still used by a small portion of people who would protect against any enemies. These blackout incidents would begin at 3:00 PM and usually end around 3:30 PM.
On 19 April 2013, the entire city of Boston was locked down and all public transportation stopped during the manhunt for Dzhokhar and Tamerlan Tsarnaev, the suspects of the 2013 Boston bombings, while the town of Watertown was under heavy-armed police and SWAT surveillance, as well as systematic house-to-house searches. 
- Digital lockdown, a block of all outward flows of information on a computer, including Internet access and internal applications, in order to prevent the spread of viral infections and glitches in the computer, or to prevent a computer hijacker from stealing information.
|Look up lockdown in Wiktionary, the free dictionary.|
- Lockdown Policy from California Hospital Association. Retrieved December 2012
- Lockdown Policy at Iroquois Healthcare Alliance. Retrieved December 2012
- Cause for UBC Lockdown still uncertain but initial posting may reveal some clues
- "Police increase presence at UBC following lockdown"
- "Threat prompts lockdown at UBC"
- "NORTH YORK: Two charged after George S. Henry Academy lockdown"
- "Teen arrested in connection with school lockdown"
- This Is What It Looks Like When the Police Shut Down a City, The Atlantic Wire, 19 Apr 2013. Retrieved Jun 2013.
- A Town Under Siege: Watertown Residents Describe Life Under Lockdown, Time, 19 Apr 2013. Retrieved Jun 2013.
- Boston faces lockdown as police hunt for marathon bombing suspect, The Guardian, 19 April 2013. Retrieved 19 April 2013.