An interjection is a word which tells some sudden or emotional feeling.

Interjections show excitement or emotion. They are not grammatically related to the rest of the sentence.

Oh!
Oh! God help me

Wow!
Wow! What an overwhelming dance.

Hurry!
Hurry! We won the match.

Hello!
Hello! What is the matter?

Hush!
Hush! Don't make noise.

Alas!
Alas! He demised.

What!
What! A melodious tune.