Interjection

An interjection or exclamation describes a noun without a grammatical connection with the rest of the sentence and simply expresses emotion on the part of the speaker, although most interjections have clear definitions. Filled pauses such as uh, er, um, are also considered interjections. Interjections are generally uninflected function words and have sometimes been seen as sentence-words, because they can replace or be replaced by a whole sentence (they are holophrastic). Sometimes, however, interjections combine with other words to form sentences, but not with finite verbs. When an exclamation point is not needed, a comma can take the place.
Interjections are used when the speaker encounters events that cause these emotions — unexpectedly, painfully, surprisingly, or in many other sudden ways. However, several languages have interjections that cannot be related to emotions.
The word "interjection" literally means "thrown in between" from the Latin inter ("between") and iacere ("throw").
Interjections are words used to express strong feeling or sudden emotion. They are included in a sentence usually at the start to express a sentiment such as surprise, disgust, joy, excitement, or enthusiasm.

Conventions like Hello, Bye, and Goodbye are interjections, as are exclamations like Cheers! and Hurray!. In fact is like a noun or an a pronoun, very often they are characterized by exclamation marks depending on the stress of the attitude or the force of the emotion they are expressing. Well can also be used as an interjection, for example when put at the beginning of a sentence. Much profanity (expletive) takes the form of interjections. Some linguists consider the pro-sentences yes, no, amen and okay as interjections, since they have no syntactical connection with other words and rather work as sentences themselves. Expressions "Excuse me!", "Sorry!", and similar ones often serve as interjections. Interjections can be phrases or even sentences, as well as words, such as "Oh!" or "Wow!".