What is really great about Percy Jackson and the Olympians: The Lightning Thief is that its fiction teaches readers about mythology. While the author takes some liberties with the source material, he does put down an effective set of base knowledge.
In my edition, Percy is told about the master bolt on page 141. Chiron tells Percy that Percy's father and Zeus are in the middle of the biggest fight they have had in hundreds of years. Chiron says that they are fighting over a valuable stolen lightning bolt. Percy isn't sure what to think of that announcement, so he nervously laughs, and Chiron passionately describes exactly what the master bolt is.
Chiron says that Zeus's master bolt is the "symbol of his power." The master bolt is also the pattern after which all other lightning bolts are formed from. He adds that the master bolt is more than just a symbol. It was the first weapon that Cyclopes made to be used by the gods in the war against the Titans. Readers are also told that the power contained within the master bolt is enough to make human hydrogen bombs equivalent to "firecrackers." It is indeed a powerful weapon because it was instrumental in forcing Kronos from his throne. It also "sheered the top off Mount Etna" which is a really cool piece of geologic information since Mount Etna is a very active volcano.