异乎寻常 is a four-character idiom meaning 'unusual' or 'extraordinary'. It literally means 'different from the ordinary' (异=different, 乎=at/than, 寻常=ordinary). It can be used as a predicate (e.g., 这种情况异乎寻常 'This situation is unusual') or as an adverb with 地 before adjectives to mean 'unusually' (e.g., 他异乎寻常地安静 'He is unusually quiet'). It is more formal than 特别 or 非常 and is common in written and formal spoken Chinese. Note: the correct pinyin is 'yì hū xún cháng', but the input lists 'yì hū xín' which appears to be a truncation.