Inductive effect is an effect that causes permanent displacement of electrons involved in covalent bond formation towards a more electronegative element. If a covalent bond is formed between carbon and an atom that is electropositive in nature, then the electrons involved in the bond formation will be pushed towards carbon imparting a small negative charge on carbon.
The effect in which ? electrons are transferred from a multiple bond to an atom, or from a multiple bond to a single covalent bond or lone pair (s) of electrons from an atom to the adjacent single covalent bond is called mesomeric effect or resonance effect or simply as M-effect. In case of the compound with conjugated system of double bonds, the mesomeric effect is transmitted through whole of the conjugated system and thus the effect may better be known as conjugative effect.