疑问句 (yíwènjù) means 'interrogative sentence' — a term you'll encounter in Chinese grammar study. The main types: 吗 questions, 呢 questions, and question-word questions (谁, 什么, 哪).
usage
毫无疑问 (háo wú yíwèn) is a set phrase meaning 'without any doubt' — equivalent to English 'undoubtedly.'