Keeping the name clean: [2 + 2] photocycloaddition.

Crossed [2 + 2] photocycloaddition is a specific case of intramolecular photocycloaddition reaction. Recently, the term "crossed [2 + 2] photocycloaddition" is interchangeably used to represent intermolecular [2 + 2] photocycloaddition reactions of two dissimilar double bonds/alkenes. To avoid confusion and to help researchers use the correct terminologies, this perspective clarifies the terminology used for different [2 + 2] photocycloaddition processes based on prior literature with the hope of establishing a standard for addressing the diverse set of photocycloaddition reactions that will be helpful to the chemical community.