Electrophile Those species which are deficient in electron or which can accept the pair of electron are called electrophile. They are either positively charged or neutral molecule. They are also called Lewis acid.
Example H+,H3O+,NO2+,SO3,BF3,AlCl3, etc.
Nucleophile Those species which are rich in electron or which can donate a pair of electron are called nucleophile. They are also called Lewis base. They are either negatively charged or neutral molecule.
Example AlCl3 is a electrophile because in the AlCl3 molecule the central atom is present with incomplete octet. It is electron deficient.
While H2O,NH3 and C2H5NH2 are nucleophile because in these molecules one of the atom has got at least one lone pair of electrons.