It is a masculine singular noun, meaning "the number three".
It can be used in a variety of contexts, such as:
* Describing a quantity: "Il y a le trois amis." (There are three friends.)
* Referring to a specific item: "Le trois est mon chiffre préféré." (Three is my favorite number.)
* As part of a sequence: "Le un, le deux, le trois." (One, two, three.)
Note: In some contexts, "le trois" might be used to refer to "the third" (like "le troisième"). However, this is not the most common use of the phrase.