Flavan-3-ols (sometimes referred to as flavanols) are a class of flavonoids that use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton. These compounds include the Catechins and the catechin gallates.
Flavanols (with an "a") are not to be confused with flavonols (with an "o"), another class of flavonoids.