Giant stars are massive stars that have expanded and cooled after exhausting the hydrogen in their cores. They are significantly larger than the Sun and can be hundreds of times its diameter. These stars are often classified into two main types: red giants and blue giants, depending on their temperature and color. As they evolve, giant stars undergo various changes, including the fusion of heavier elements in their cores. Eventually, they may shed their outer layers, creating beautiful nebulae, while the core can collapse into a supernova or become a neutron star or black hole.