ex·po·si·tion / ˌekspəˈzishən/ • n. 1. a comprehensive description and explanation of an idea or theory: an exposition and defense of Marx's writings. ∎  Mus. the part of a movement, esp. in sonata form, in which the principal themes are first presented. ∎  the part of a play or work of fiction in which the background to the main conflict is introduced.2. a large public exhibition of art or trade goods. ∎ archaic the action of making public; exposure: the country squires dreaded the exposition of their rustic conversation.DERIVATIVES: ex·po·si·tion·al / -zishənl/ adj.

exposition.
1. In sonata form, the first section of a comp. in which the prin. themes are expounded before they are developed.

2. In fugue the first statement of the subject by all the ‘voices’ in turn.