What is Inductive effect?

The inductive effect is the shift of electron density along $\sigma$ bonds towards an electronegative atom or group. An attracting group (F, Cl, O, $\ce{NO2}$, $\ce{CF3}$) has a $-I$ effect; alkyl groups and negatively charged atoms push electrons, a $+I$ effect. The effect weakens quickly with the number of bonds in between.