In the sentence "He said he did well on the test," what part of speech is "well"?

In the sentence "He said he did well on the test," "well" functions as an adverb. Adverbs modify verbs, adjectives, or other adverbs, often explaining how an action is performed. Here, "well" describes the manner in which he did on the test, indicating that his performance was good.

In terms of context, it's important to distinguish "well" from other parts of speech. It is not an adjective, as adjectives describe nouns and noun-like pronouns. Similarly, "well" is not a noun; it does not name a person, place, thing, or idea. Lastly, it is not a pronoun, which replaces nouns and stands in for them in a sentence. Therefore, identifying "well" as an adverb is accurate, as it gives further information about the action of the verb "did."