An interjection is a word or phrase showing emotion or surprise which has no grammatical relationship to any other words or part of a sentence.
They are often punctuated by exclamation points and are used infrequently.
It is best to avoid the use of them in formal writing other than direct quotations.
In most dictionaries the abbreviation interj. means "interjection."
Examples: Ouch, Hey, Oh my, Wow