膨胀 (péng zhàng) is a general verb meaning 'to expand, inflate, or swell', used for gases, prices, body parts, and abstract concepts. It is broader than 涨 (zhàng), which focuses on volume increase (e.g., prices, swelling), and 肿 (zhǒng), which is limited to body swelling. For expanding territory or influence, use 扩张 (kuò zhāng).