Salt bridge: A salt bridge consists of a glass U-tube containing semi-solid paste of either KCl, KNO3 , etc which connects two half cells.
Role of salt bridge:
A salt bridge's primary role is to help in the maintenance of electrical neutrality.
If salt bridges are not present used, the reaction will most likely continue and the solution in half electrodes will accumulate a negative charge. Similarly, electrodes in the other half would accumulate a positive charge.
As a result, the reaction will stop and no electricity will be generated.