Immature describes someone or something that hasn't fully developed yet, either physically or in behavior and judgment. A green, immature strawberry needs more time on the plant before it's ready to eat. An immature tree is still young and growing.

When describing people, immature usually means acting younger than your age in ways that cause problems. An immature student might giggle during serious moments, make silly noises when the teacher is talking, or throw tantrums when things don't go their way. It's the kid who can't handle losing a game without getting angry, or who blames everyone else when something goes wrong.

Everyone acts immature sometimes, especially when tired or upset. The difference is whether someone learns from experience and gradually handles situations better. A seven-year-old crying over a lost toy isn't being immature because that's normal for their age. A twelve-year-old doing the same thing is showing immature behavior because they should have developed better ways to handle disappointment by then.

The opposite of immature is mature, which describes someone who thinks before acting, considers how their behavior affects others, and handles difficulties without falling apart. Growing up physically happens automatically, but developing mature judgment takes practice and effort.