The definition of the intermediate

The transmission of wave energy needs the quasi elastic collision of some basic particles of matter. The composition, shape, density and motion state of this material determine the transmission direction and speed of wave energy. This material that plays a decisive role in the propagation of wave is called the medium of this wave

When one substance exists in another substance, the latter is the medium of the former.
Some wavy motions, such as sound wave and light wave, are called the medium of these wavy motions. Also called medium.
Media are divided into optical media, dielectric media, mechanical wave media, magnetic media and so on
In addition, media also exist outside the physical definition, such as language, text, mode of communication and so on