An exhibition, in the most general sense, is an organized presentation and display of a selection of items. In practice, exhibitions usually occur within museums, galleries and exhibition halls, and World's Fairs.
Exhibitions include (whatever as in major art museums and small art galleries; interpretive exhibitions, as at natural history museums and history museums), for example; and commercial exhibitions, or trade fairs.
The word "exhibition" is usually, but not always, the word used for a collection of items. Sometimes "exhibit" is synonymous with "exhibition", but "exhibit" generally refers to a single item being exhibited within an exhibition.
Source: Wikipedia