It's a word that expresses strong emotion or surprise, often used to call out or get attention.
Here's why:
* It stands alone: Interjections are independent words that don't grammatically connect to the surrounding sentence.
* It expresses emotion: "Hallooh" conveys excitement, surprise, or a call for attention.
While it might resemble a verb in some contexts, it's not grammatically acting as a verb in the traditional sense.