To fill or block a hole or gap. He used a piece of cloth to plug the leak in the pipe.
To promote or advertise something, especially in a persistent or enthusiastic manner. The author went on several talk shows to plug her new book.
To connect an electrical device to a power source or another device. She plugged the charger into the wall socket to charge her phone.
To shoot or hit someone or something with a bullet. The detective warned the criminal that he would plug him if he didn't drop the weapon.