Addition: Electrophilic
Electrophilic addition is a stepwise process. The first step involves a electrophilic Lewis acid (often with net positive charge) complexing with a pi-system to generate a carbenium ion centre which subsequently complexes with a nucleophilic Lewis base.

Note that it can be difficult to distinguish between nucleophilic and electrophilic addition.

For more information look in the Chemogenesis webbook section on addition reactions.