Teenager, or teen for short, is a term used to describe a human who falls within the age range of 13 to 19 years old. This period of time, also known as adolescence, is characterized by major physical, cognitive, and social development and ultimately functions as the transitional period between childhood and adulthood. The start of one’s teen years usually coincides with the onset of puberty, a notoriously awkward period of physical development that lasts several years, and gradually results in near complete independence from the teenager’s legal guardian(s) as they enter into adulthood.