Surfactants in solution are often
association colloids, that is, they tend to form aggregates of
colloidal dimensions, which exist in equilibrium with the molecules or ions from which they
are formed. Such aggregates are termed micelles.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1140