Cosmonauts are astronauts from Russia or the former Soviet Union who are trained to travel into space. They conduct scientific research, perform experiments, and operate spacecraft. The term "cosmonaut" comes from the Greek words for "universe" and "sailor," reflecting their role in exploring outer space. To become a cosmonaut, individuals must undergo rigorous training, which includes physical fitness, technical skills, and simulations of space missions. They often work on missions aboard the International Space Station (ISS) and contribute to our understanding of space and its effects on the human body.