Sound- a : a particular auditory impression : TONE b : the sensation perceived by the sense of hearing c : mechanical radiant energy that is transmitted by longitudinal pressure waves in a material medium (as air) and is the objective cause of hearing.

Design- the arrangement of elements or details in a product or work of art.
definitions from: http://www.m-w.com/

Sound Design for the theatre is comprised of many elements. At its core, Sound Design involves the processof meeting the auditory requirements for a particular theatrical production. Many times this involves capturing sound recordings or creating sound effects, sonic environments, and music as dictated by a dramatic script and the theatrical production's needs. Sometimes it involves sound reinforcement through the use electronic equipment or acoustic consideration. Often, a combination of these elements is required. The University of Virginia's Department of Drama offers courses in Sound Design. In these courses, students are introduced to the art of creating sonic material for theatre and other media and the process of designing with sound.