According to Muji's website:
What is MUJI?
MUJI is not a brand whose value rests in the frills and "extras" it adds to its products.
MUJI is simplicity - but a simplicity achieved through a complexity of thought and design.
MUJI's streamlining is the result of the careful elmination and subtraction of gratuitous features and design unrelated to function.
MUJI, the brand, is rational, and free of agenda, doctrine, and "isms." The MUJI concept derives from us continuously asking, "What is best from an individual's point of view?"
MUJI aspires to modesty and plainness, the better to adapt and shape itself to the styles, preferences, and practices of as wide a group of people as possible. This is the single most important reason people embrace MUJI.
MUJI - in its deliberate pursuit of the pure and the ordinary - achieves the extraordinary.