An 18 year old female patient complains of prominent upper front teeth while smiling. Extra-oral examination reveals an acute nasolabial angle. Intraoral examination shows a Class II incisor relation with 5 mm overjet and Class I molar relation. Orthodontic therapy is initiated with first premolar extractions in all quadrants. The extraction space is to be closed by an equal amount of anterior teeth retraction and posterior teeth protraction. The anchorage requirement of this patient can be classified as:
In moderate anchorage, the extraction space needs to be closed by an equal amount of retraction of anterior teeth and protraction of posterior teeth.
In minimum anchorage, all or at least 75%—of the extraction space is closed by protraction of the posterior teeth. This is nearly the opposite of maximum anchorage mechanics.
Key concept:

Retraction of anterior teeth (maximum anchorage) 
Protraction of posterior teeth (minimum anchorage) 
A combination of both (moderate anchorage)

Biomechanics in Orthodontics: Principles and Practice, R. Nanda page 146
Critical anchorage
Minimum anchorage
Moderate anchorage
Maximum anchorage