朴素 (pǔ sù) describes something plain, simple, and unadorned — often for clothing, lifestyle, or writing style that avoids decoration or luxury. It differs from 简单 (jiǎn dān, 'simple, not complicated'), which focuses on lack of complexity, and from 朴实 (pǔ shí, 'simple and unpretentious'), which emphasizes a person's honest character. 朴素 is the main word for 'plain' in appearance and living.