Longman Dictionary of Contemporary English
WordNet
n. young adults (a generational unit) considered as a cultural class or subculture
Wikipedia
Youth culture is the way adolescents live, and the norms, values, and practices they share. Culture is the shared symbolic systems, and processes of maintaining and transforming those systems. Youth culture differs from the culture of older generations.
Elements of youth culture include beliefs, behaviors, styles, and interests. An emphasis on clothes, popular music, sports, vocabulary, and dating set adolescents apart from other age groups, giving them what many believe is a distinct culture of their own. Within youth culture, there are many distinct and constantly changing youth subcultures. These subcultures' norms, values, behaviors, and styles vary widely, and may differ from the general youth culture. Understanding what adolescents think and do is fundamental to understanding the relationship between structure and agency, social patterns and individual action.