1 [uncountable and countable]
when someone goes around different parts of an area at regular times to check that there is no trouble or danger
police on patrol in the city centre
The security forces increased their patrols in the area.
a group of police, soldiers, vehicles, planes etc sent out to search a particular area:
a US border patrol
patrol boat/car (=used by the army or police)
a small group of boy scouts or Guides