The defining characteristics of these forms opera vs symphony

Opera incorporates many of the elements of spoken theatre, such as acting,scenery, and costumes and sometimes includes dance. The performance is typically given in an opera house, accompanied by an orchestra or smaller musical ensemble. Opera is part of the Western classical music tradition.

symphony, a lengthy form of musical composition for orchestra, normally consisting of several large sections, or movements, at least one of which usually employs sonata form (also called first-movement form).