An interjection is a word or expression that occurs as an utterance on its own and expresses a spontaneous feeling or reaction. It is a diverse category, encompassing many different parts of speech, such as exclamations (ouch!, wow!), curses (damn!), greetings (hey, bye), response particles (okay, oh!, m-hm, huh?), hesitation markers (uh, er, um), and other words (stop, cool). Due to its diverse nature, the category of interjections partly overlaps with a few other categories like profanities, discourse markers, and fillers. The use and linguistic discussion of interjections can be traced historically through the Greek and Latin Modistae over many centuries.