An exclamation is a sentence that generally expresses emotion. English examples include Wow! and What a shame!. They are not necessarily grammatical sentences and marked by strong intonation and punctuation (ex. Exclamation point). In modern grammar there are exclamatory sentences that usually start with “what” and “how.” There are also phrases that can be exclamative, but not an exclamation such as “How the hell do I know?”
Matthews, P. H. The Concise Oxford Dictionary of Linguistics. Oxford: Oxford University Press, 1997.
Crystal, David, and David Crystal. The Penguin Dictionary of Language. London: Penguin, 1999.