The effect of the sigma electron displacement towards the more electronegative atom by which one end becomes positively charged and the other end negatively charged is known as the inductive effect. The -I effect is a permanent effect & generally represented by an arrow on the bond.
However, some groups, such as the alkyl group, are less electron-withdrawing than hydrogen and are therefore considered as electron-releasing/ electron-donating groups. This is electron-releasing character and is indicated by the +I effect. In short, alkyl groups tend to give electrons, leading to the induction effect. However, such an effect has been questioned.
As the induced change in polarity is less than the original polarity, the inductive effect rapidly dies out and is significant only over a short distance. Moreover, the inductive effect is permanent but feeble since it involves the shift of strongly held σ-bond electrons and other stronger factors may overshadow this effect.