Here's why:
* It names a thing: A season is a period of time marked by specific weather patterns.
* It can be used as the subject of a sentence: "The season is changing."
* It can be used as the object of a verb: "I love the fall season."
However, "season" can also function as a verb in some cases, meaning "to add flavor or seasoning to."
For example: "She seasoned the dish with salt and pepper."