A straight play is a term used to describe a form of theatrical production featuring spoken drama.
While music is one of Aristotle's six elements of theatre, a straight play does not usually include singing. However, some singing may be used for special characterisation. (Usually, the term straight play does not include the Theatre of the Absurd.) Straight play is commonly used to differentiate a non-musical a musical form.
Aristotle's six elements of theatre or play are known as plot, character, thought (theme), diction, music, and spectacle. (reference from this page)