Definition of proposition:

part of speech: noun

That which is proposed or offered for consideration or acceptance; an offer of terms; in math., a theorem or problem for demonstration or solution; that which is offered or affirmed; the first part of a poem or discourse in which the subject of it is stated; in gram. and logic, a sentence, or part of one, consisting of a subject, a predicate, and a copula; a form of speech in which the predicate is affirmed or denied of a subject.