The material through which light travels is called a medium.

Here are some examples of mediums:

* Air: This is the most common medium we experience.

* Water: Light travels slower through water than air, causing refraction (bending of light).

* Glass: Light also travels slower through glass than air, which is why we use glass lenses in eyeglasses and cameras.

* Vacuum: Light can also travel through a vacuum, which is the absence of any matter. This is how light reaches us from the sun and stars.

Let me know if you have any other questions!