Interjection is a big name for a little word. They have no real grammatical value but we use them quite often, usually more in speaking than in writing.When interjections are inserted into a sentence, they have no grammatical connection to the sentence. An interjection is sometimes followed by an exclamation mark (!) when written.

For example:
1. Hurray! Our team has won the match.
2. Hey! Are you serious?
3. Alas! John’s father died yesterday.
4. Hi! Where have you been?
5. Oh! The place is so crowded.