Fusion energy is the energy released during nuclear fusion reactions, a process involving the combination of light atomic nuclei under extreme conditions to form heavier ones. As a research field and engineering concept, it investigates the principles, methods, and technologies required to achieve controlled, sustained nuclear fusion and convert the resulting energy into usable forms, focusing on plasma physics, confinement strategies (such as magnetic or inertial confinement), materials science, and reactor design. This concept is highly significant for its potential to provide a virtually unlimited, low-carbon, and inherently safe global energy source.