ˌhomeland seˈcurity BrE AmE noun [uncountable]
actions taken by the US government after the ↑ terrorist attacks of September 11th, 2001 to prevent ↑ terrorism within the US. These actions include watching people who are thought to be involved in ↑ terrorist activities, and putting them in prison if necessary. They also include preparations for using the army, police, doctors etc immediately if there is a terrorist attack.