"Extrusive" refers to a type of igneous rock that forms when molten lava cools and solidifies on the Earth's surface. This process occurs during volcanic eruptions, where lava flows out of a volcano and spreads across the land. As the lava cools quickly, it creates fine-grained rocks, such as basalt and pumice. Extrusive rocks are often characterized by their glassy texture and small crystals, which result from rapid cooling. They can also form various volcanic features, including lava plateaus and volcanic islands. Understanding extrusive rocks helps geologists learn about volcanic activity and the Earth's geological history.