Design
Design is the creation of a plan or convention for the construction of an object, system or measurable human interaction (as in architectural blueprints, engineering drawings, business processes, circuit diagrams, and sewing patterns). Design has different connotations in different fields (see design disciplines below). In some cases, the direct construction of an object (as in pottery, engineering, management, coding, and graphic design) is also considered to use design thinking.
Interior Design
Interior design is the art and science of enhancing the interior of a building to achieve a healthier and more aesthetically pleasing environment for the people using the space. An interior designer is someone who plans, researches, coordinates, and manages such projects. Interior design is a multifaceted profession that includes conceptual development, space planning, site inspections, programming, research, communicating with the stakeholders of a project, construction management, and execution of the design.
Decoration
You may have a throne at the royal court, with beautiful decorations and soft carpets, all sorts of luscious fruits and beautiful gardens, the excitement of the chase and princely pleasures - but still, the mind is not made happy by such illusory diversions.
Guru Granth Sahib in: Sikhism Religion of the Sikh People: Sri Guru Granth Sahib Translation, p. 173
Interior
What is necessary, after all, is only this: solitude, vast inner solitude. To walk inside yourself and meet no one for hours—that is what you must be able to attain.
Rainer Maria Rilke, Letters to a Young Poet, 6