坦诚 (tǎn chéng) is an adjective meaning 'sincere' or 'open-hearted,' describing someone who speaks and acts with honesty, transparency, and emotional authenticity. The character 坦 (tǎn) conveys openness, levelness, and lack of concealment—like a flat, unobstructed field—while 诚 (chéng) means 'sincerity' or 'genuineness,' rooted in integrity and truthfulness. Together, they emphasize not just honesty in words, but also emotional vulnerability and moral straightforwardness.

This word is commonly used in interpersonal contexts—such as friendships, romantic relationships, or workplace communication—to praise or encourage authentic expression. It often appears in phrases like 坦诚相待 (tǎn chéng xiāng dài, 'treat each other sincerely') or 坦诚交流 (tǎn chéng jiāo liú, 'open communication'). While it carries a positive, mature connotation, it’s more formal than colloquial terms like 真实 (zhēn shí) and implies both courage and trustworthiness.