Interjections (sometimes called exclamations) are used to express strong feeling or emotion, usually that occurs quickly.

Don’t touch that!

Other links for Interjections
XX List of Common Interjections
XX Definition of Interjection
XX Function of Interjection

For more information about the different parts of speech take a look at

The Basics of English Grammar

An explanation of an interjction- including their function, type, placement and formation–