The defining feature of gamma rays (γ) is that they are?

Gamma rays (γ) are a form of electromagnetic radiation that carries a high amount of energy. This distinguishes them from other forms of radiation, such as alpha and beta particles, which consist of actual particles rather than waves. Gamma rays are emitted during radioactive decay processes, often alongside alpha and beta particles, but what sets them apart is their nature as electromagnetic waves possessing the highest energy within the electromagnetic spectrum.

Their high energy allows gamma rays to penetrate materials more effectively than other types of radiation, making them useful in various applications such as medical imaging and cancer treatment. This characteristic of being high-energy electromagnetic radiation, therefore, defines gamma rays and separates them from other radiation types, which may involve particles or lower energy levels.