Tween

Preadolescence, also known as pre-teen or tween, is a stage of human development following early childhood and preceding adolescence. It commonly ends with the beginning of puberty, but may also be defined as ending with the start of the teenage years. For example, dictionary definitions generally designate it as 10–13 years. Preadolescence can bring its own challenges and anxieties.

Although dictionary definitions generally define preadolescence as ranging from age 10 to 13 years, it may also be defined as the period from 9 to 14 years. While known as preadolescent in psychology, the terms preteen, preteenager or tween are common in everyday use. A preteen or preteenager is a person 12 and under. Generally, the term is restricted to those close to reaching age 12, especially age 11.Tween is an American neologism and marketing term for preteen, which is a blend of between and teen. People within this age range are variously described as tweens, preadolescents, tweenies, preteens, pubescents, junior highers or tweenagers.

The term tween was previously used in J. R. R. Tolkien's 1954 novel The Lord of the Rings to refer to hobbits in their twenties: "tweens as hobbits called the irresponsible twenties between childhood and the coming of age at thirty-three." In this context, the word is really either a shortened version of between or a portmanteau of teen and twenty, and in either case has no connection to teens, preteens or the American marketing niche.

The point at which a child becomes an adolescent is defined by the onset of puberty or by the beginning of the teenage stage. Adolescence is also viewed as ending with the teenage stage. However, in some individuals (particularly females), puberty begins in the preadolescence years, and adolescence may extend a few years beyond the teenage years in others (typically males). Studies indicate that 'the onset of puberty has been one year earlier with each generation since the 1950s.'

...
Wikipedia