服气 means 'to be convinced' or 'to accept' a viewpoint or outcome, often after initial resistance or in a competitive context. It's more colloquial than 确信 or 坚信 (firm belief) and focuses on conceding to someone else's superiority or argument, especially in the common negative form 不服气 (unconvinced, not accepting). Unlike 相信 (general belief), 服气 implies a sense of yielding or admiration.