sp2 hybridization occurs when one s orbital and two p orbitals combine to form three equivalent hybrid orbitals, each with 33.3% s character and 66.7% p character, often resulting in a trigonal planar geometry with 120-degree bond angles. This type of hybridization is commonly found in molecules with double bonds, such as alkenes, where it allows for the formation of a sigma bond and a pi bond through lateral overlap of unhybridized p orbitals.