Interjections are words or phrases that express strong emotion or surprise. They are often used to express:
* Surprise: Oops! I dropped my phone.
* Regret: Oops, I forgot to lock the door.
* Acknowledgement of a mistake: Oops, I think I made a mistake.
While "oops" can sometimes be used in a more casual way, it's fundamentally an interjection because it stands alone and expresses a distinct emotion.