低下 means 'low' in the sense of inferior status, quality, or degree — it carries a negative judgment (e.g., poor quality, humble birth). It is distinct from neutral 低 (dī) for height/price, from emotional 低落 (dīluò, 'downcast'), and from the positive humility words 谦逊/谦虚/虚心 (which describe a respectful, unassuming attitude, not low value).