Social system and stage of human development characterized by common ownership of the means of production and the absence of social classes; political and economic ideology or doctrine established by 马克思 mǎ​kè​sī and 恩格斯 ēn​gé​sī

a young person or young people; the period of time between childhood and maturity; youthful years

(abbreviation) specifically refers to the Communist Youth League of China