Small groups or individual units are deployed from a larger formation to achieve a specific objective and then return.
The duration of a patrol will vary from a few hours to several weeks depending on the nature of the objective and the type of units involved.
A combat patrol is a group with sufficient size (usually platoon or company) and resources to raid or ambush a specific enemy.
Clearing patrols are often undertaken on the occupation of a location, and during stand to in the transition from night to day routine and vice versa.
This type of patrol is used by armored formations in desert theaters, and also by ground troops operating in urban areas.