Chengyu are a type of traditional Chinese idiomatic expressions, most of which consist of four Chinese characters. Chengyu were widely used in Literary Chinese and are still common in written vernacular Chinese writing and in the spoken language today. According to the most stringent definition, there are about 5,000 chengyu in the Chinese language, though some dictionaries list over 20,000. Chengyu are considered the collected wisdom of the Chinese culture, and contain the experiences, moral concepts, and admonishments from previous generations of Chinese speakers. Chengyu still play an important role in Chinese conversation and education. Chengyu are one of four types of formulaic expressions, which also include collocations, two-part allegorical sayings called xiehouyu, and proverbs.