Allosteric control occurs when a small regulatory molecule causes the inhibition or activation of an enzyme at an allosteric site rather than the active site (the region of the enzyme that binds to substrates, where catalytic activity occurs). Another name for allosteric control is allosteric stimulation.
Allosteric control causes a change in the shape of the enzyme at the active site, resulting in a change of formation of the usual complex between the enzyme and its substrate - the compound upon which the enzyme acts to create a product. The changes modify the enzyme's ability to catalyze a reaction. Allosteric control is the basis of an important theory known as the Induced-Fit theory.