About children who are around eleven or twelve — just before the teen years (thirteen to nineteen). Shops sell preteen clothes; writers talk about the preteen years. You can also call the child a preteen: “She is still a preteen.” It sits in that in-between stretch: not a little kid, not a teenager yet. Though actually, people are a little loose with the ages. Some speakers stretch it down to nine or ten; the tidy dictionary picture is eleven and twelve. The word is everyday and very common in American English; other places understand it at once. It is not a medical term, just a life-stage word.