Master Bolt

The Master Bolt is the symbol of Zeus' power from which all other lightning bolts are patterned. It is a two-foot-long cylinder of high-grade celestial bronze capped on both ends with god-level explosives. It makes mortal hydrogen bombs look like firecrackers (According to Chiron). When it is activated, the cylinder emits a more classical-looking lightning bolt. The master bolt is the first and most powerful weapon that the Cyclops made for a god. The purpose of it was to become Zeus' main weapon and to help battle the Titans during the First Olympian War. The Master bolt sheared the top off of Mount Etna and hurled Kronos from his throne. It is the most powerful weapon in the world.

The Lightning Thief
In The Lightning Thief, Percy is accused by Zeus of stealing his master bolt for Poseidon. Because of this, Percy goes on a quest to retrieve the master bolt. Luke Castellan was actually the one who stole the bolt. Luke said "You wouldn't believe how easy it was to steal the master bolt". Ares caught him but didn't turn him over. Percy accused Hades at first but Hades denied it and said that his Helm of Darkness was also gone. Percy retrieves both items and returns them safely after fighting Ares who was the real thief.

The Last Olympian
In The Last Olympian, Zeus uses it to attack Typhon, but it just makes him stumble backwards, only injuring the beast slightly and making it more angry.

Film
In the movie adaptation of The Lightning Thief, it is portrayed as a shaft of crystallised lightning that can shoot bolts of lightning.