What part of speech is the word good?

"Good" can be several parts of speech, depending on its function in a sentence:

* Adjective: Describing a noun. Example: "He is a good student."

* Adverb: Modifying a verb, adjective, or another adverb. Example: "He did good on his test." (Note: this usage is considered non-standard in formal writing)

* Noun: Meaning "something good". Example: "There is good in everyone."

* Interjection: Expressing approval. Example: "Good! Let's get started."

The part of speech is determined by its role in the sentence.