What is what part of speech is really?

The word "really" can function as an adverb, an interjection, or an intensifier.

As an adverb, "really" is used to emphasize the truth or accuracy of a statement. For example, "I really enjoyed the concert."

As an interjection, "really" can be used to express surprise, disbelief, or strong emotion. For example, "Really? I didn't know that!"

As an intensifier, "really" is used to strengthen or emphasize a particular quality or characteristic. For example, "She is really talented."