An interjection is a word or phrase that expresses strong emotion or feeling. It is often used independently of the main sentence, and can stand alone.
Here are some examples:
* Wow! (Surprise)
* Ouch! (Pain)
* Hey! (Attention)
* Ugh! (Disgust)
* Hooray! (Joy)
Interjections are often used in informal writing and speech, but they can also be used in formal contexts to add emphasis or emotion.