A youngster is a young person, typically a child or teenager. When a teacher says “listen up, youngsters,” she's addressing the kids in her class. When a grandfather talks about “youngsters these days,” he might be referring to anyone from elementary schoolers to high school students, or sometimes even young adults.

The word has a friendly, informal feeling to it. Adults often use it affectionately when talking to or about young people: “You youngsters have so much energy!” A coach might call out “good hustle, youngster!” to encourage a player. In stories set in earlier times, you'll often see adults addressing children as youngsters.

While youngster usually refers to kids and teens, exactly who counts as a youngster depends on who's speaking. To a 70-year-old veteran, a 30-year-old might still seem like a youngster. To a fifth grader, a kindergartner is definitely a youngster. The word captures a relative idea: someone younger than the speaker, with youth and energy to spare.