A "generation" primarily refers to all people born and living around the same time, typically representing an average period of 20-30 years for children to grow up and have their own. Beyond kinship, it also describes "social generations"—age cohorts sharing similar significant cultural experiences. While the idea has ancient roots, its modern application to broader social groupings, as formally defined by Emile Littré in 1863, gained prominence in the 19th century, influenced by modernization and an increasing awareness of social change. The average length of a familial generation in developed nations has notably extended to nearly 30 years since the late 18th century, driven by factors like industrialization, urbanization, and delayed parenthood. This contrasts with less-developed nations, where it remains in the low 20s. Understanding generations is crucial for sociological analysis and recognizing societal dynamics and cultural shifts.