"Many people use the terms "interior design" and "interior decorating" interchangeably, but these professions differ in critical ways.
Interior design is the art and science of understanding people's behavior to create functional spaces within a building. Decoration is the furnishing or adorning of a space with fashionable or beautiful things. In short, interior designers may decorate, but decorators do not design.
Interior designers apply creative and technical solutions within a structure that are functional, attractive and beneficial to the occupants' quality of life and culture. Designs respond to and coordinate with the building shell and acknowledge the physical location and social context of the project. Designs must adhere to code and regulatory requirements and encourage the principles of environmental sustainability."
Quote from NCDIQ