An interjection are all those words that you can just say by themselves and add an exclamation point to. "Wow!" "OY!" "D'oh!" Those are all interjections. An exclamation includes that, but can be a complete sentence as well. "Get to work!" So...
An interjection is a part of speech that usually has no grammatical connection with the rest of the sentence and simply expresses emotion on the part of the speaker, although most interjections have clear definition....