Cofactor may refer to any of the following:

• Minor (linear algebra) as an alternative name for the determinant of a smaller matrix than that which it describes
• Cofactor (biochemistry) is a substance that needs to be present in addition to an enzyme for a certain reaction to take place.
• Shannon cofactor is a derived function of another function, a notion useful in computer science and mathematics.
• In epidemiology, a cofactor is a condition that exacerbates the effects of another condition; for instance, while chlamydia infection on its own will not cause cervical cancer, it increases the risk that HPV infection will do so.

Cofacteur