What is a discrete bundle of electromagnetic (or light) energy called?

The term that specifically refers to a discrete bundle of electromagnetic (or light) energy is "photon." Photons are elementary particles that represent the smallest possible unit of light and other forms of electromagnetic radiation. They possess both particle-like and wave-like properties, which is a fundamental concept in quantum mechanics.

Understanding photons is essential in fields such as optics, telecommunications, and even quantum computing, as they are the carriers of light energy. While other terms related to electromagnetic energy exist, such as waves, particles, and quanta, they do not precisely capture the unique characteristics of light energy in its discrete form. "Wave" refers to the wave-like propagation of light, while "particle" is a broader term that can encompass various entities within physics. The term "quantum" generally relates to the discrete units of energy levels but does not specifically denote the packets of light energy, thus making "photon" the most accurate choice in this context.