What is what part of speech is the?

The is a determiner, specifically a definite article.

Here's a breakdown:

• Determiner: A determiner is a word that introduces a noun or noun phrase. It specifies which noun the speaker or writer is referring to.

• Definite Article: The is the definite article in English. It indicates that the noun it modifies is specific and known to the speaker and listener (or writer and reader). It implies that the noun has already been mentioned, is unique, or is otherwise clear from the context.