A giant star is a type of star that has expanded and cooled after exhausting the hydrogen in its core. These stars are much larger than the Sun and can be several times more massive. They are often found in the later stages of stellar evolution and can be classified into different types, such as red giants and blue giants, based on their temperature and color. Giant stars are significant in the universe because they play a crucial role in the formation of heavier elements through nuclear fusion. When they reach the end of their life cycle, they may explode in a supernova, contributing to the cosmic material that forms new stars, planets, and other celestial bodies, including black holes and neutron stars.