The Lost Generation refers to a demographic cohort of people born approximately between 1883 and 1900, who came of age during World War I. The term is often used to describe the widespread disillusionment and moral alienation felt by many young people, especially intellectuals and creatives, who experienced the traumatic impacts of the war. This generation was seen as "lost" because traditional values and ideals were shattered by the war's death and destruction, leaving many feeling aimless, cynical, and disconnected from the prewar world.

The phrase "Lost Generation" is credited to writer Gertrude Stein, who reportedly used it in speaking to Ernest Hemingway. Hemingway popularized it further by using it as an epigraph in his 1926 novel "The Sun Also Rises," to capture the spirit of disoriented and directionless survivors of the war.

The Lost Generation is notably associated with a group of American expatriate writers living and working mainly in Paris during the 1920s, including Ernest Hemingway, F. Scott Fitzgerald, John Dos Passos, and others. These writers explored themes of war trauma, societal change, material excess, alienation, and the search for meaning in their works. Their writing marked a break with traditional narrative styles, reflecting the fractured world in which they lived and influencing modernist literature.

Overall, the Lost Generation is both a historical and literary term describing those shaped by the severe cultural and psychological impact of World War I, depicting a generation struggling to find purpose in a drastically changed world.