Interjections

Interjections are words or phrases used to exclaim or protest or command. They sometimes stand by themselves, but they are often contained within larger structures.

• Wow! I won the lottery!
• Oh, I don't know about that.
• I don't know what the heck you're talking about.
• No, you shouldn't have done that.

Most mild interjections are treated as parenthetical elements and set off from the rest of the sentence with a comma or set of commas. If the interjection is more forceful, however, it is followed with an exclamation mark. Interjections are rarely used in formal or academic writing.

Credit :: www.grammar.ccc.commnet.edu