An interjection is word that we use to express strong feeling and emotion in our sentences. It has no grammatical connection to the sentence. Examples of interjections include filled pauses like er, uh, um or words such as wow!, like, oh!, well, ouch.
- This is, er, my new girlfriend.
- Mike is, um, a bit intact, you know.
- We met, like, 3 months ago.
- Oh! You didn't mention you were busy.
- Wow! I'm impressed!
As you can see, interjections are often followed by an exclamation mark: !