When we refer to the "speed of light," we are specifically talking about the speed at which electromagnetic radiation propagates through a vacuum. This speed is denoted by the symbol 'c' and is approximately 299,792,458 meters per second (or about 186,282 miles per second).
Electromagnetic radiation includes a wide range of wavelengths, spanning from radio waves to microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. All forms of electromagnetic radiation, regardless of their wavelength, travel at the same speed in a vacuum, which is the speed of light.
Photons, on the other hand, are the fundamental particles or quanta associated with electromagnetic radiation. Each photon carries a specific amount of energy corresponding to its frequency or wavelength. Photons themselves do not have a mass and always travel at the speed of light in a vacuum.
So, when we mention the "speed of light," we are generally referring to the speed at which photons or any other form of electromagnetic radiation travels in a vacuum.