An exclamative sentence is a sentence type used to express surprise about something unexpected or extraordinary.
In many European languages, exclamative sentences have special properties and are therefore treated as a special sentence type alongside declarative and interrogative sentences. It is very likely that there are also languages without a special class of exclamative sentences.
In many European languages, exclamative sentences are similar to interrogative sentences in that they use interrogative pronouns, e.g. English How big it is!