A volcano is a kind of mountain with a special secret inside: hot melted rock, called magma, deep underground. When the magma finds a way out, it erupts as red-hot lava, ash and steam. After the rock cools, it builds up around the opening - and over thousands of years, a mountain grows.
The most famous volcano in the Philippines is Mayon. It sits on the island of Luzon and has an almost perfect cone shape - many people say it is the world's most symmetrical volcano. From far away, it looks like a child has drawn the perfect triangle of a mountain on the horizon.
Volcanoes sound a bit scary, but they are also good for the country. Volcanic soil is incredibly rich in nutrients - it is one of the best soils in the world for growing things. Many of the rice fields, mango trees and vegetable gardens in the Philippines grow in soil that came from old eruptions, thousands of years ago.
Scientists watch the active volcanoes very carefully. They have machines that measure tiny movements in the ground and changes in the temperature, so that everyone gets plenty of warning if one of them looks like it might wake up. The Philippines is one of the best-watched volcano countries on Earth.