Keto-enol tautomerism is tautomerism involving an aldehyde or a ketone and an enol.

eg. 1:

eg. 2:

In keto-enol tautomerism, the aldehyde or the ketone is called the keto form and the enol is called the enol form.  In most keto-enol tautomerisms, the equilibrium lies by far toward the keto form, indicating that the keto form is usually much more stable than the enol form, which can be attributed to the feet that a carbon-oxygen double bond is significantly stronger than a carbon-carbon double bond.