Words such as "oh", or "wow", which are used to indicate an isolated emotion on the part of the speaker, without an explicit grammatical relationship to the rest of the sentence.
An interjection is a word which indicates some emotion or reaction on the part of the speaker. Conventionally, interjections have no grammatical relationship to the rest of the sentence in which they appear, and they are disfavored in formal writing.
Some common interjections include:
In addition, many swear words and vulgarities are primarily used as interjections.