Gluons are considered to be real particles. Gluons are elementary particles that mediate the strong nuclear force, which is one of the fundamental forces of nature. They are responsible for holding quarks together inside protons, neutrons, and other hadrons.
Gluons are classified as gauge bosons, similar to photons, which are the particles that mediate the electromagnetic force. Like photons, gluons are bosons and have integer spin (spin-1). They are massless particles, meaning they travel at the speed of light.
Gluons can interact with other particles that carry the strong charge, such as quarks and other gluons. These interactions are described by quantum chromodynamics (QCD), which is the theory of the strong force. In certain situations, gluons can also exist as virtual particles, appearing as intermediate particles in particle interactions or Feynman diagrams.
So, while gluons can exist as virtual particles in some contexts, they are fundamentally real particles that play a crucial role in the strong force and the interactions between quarks and other particles.