Meteorites are rocks or debris that have survived the journey through Earth's atmosphere and landed on its surface. They are valuable for scientific research as they provide information about the early history of the solar system, the formation of planets, and the composition of celestial bodies. Meteorites can be categorized into different types based on their composition, with the most common types being stony meteorites, iron meteorites, and stony-iron meteorites. Scientists study meteorites to gain insights into the formation and evolution of our solar system.