1.  teens(n = noun.time) - the time of life between the ages of 12 and 20;
is a kind of time of life
is a part of adulthood, maturity

2.  teens(n = noun.quantity) - all the numbers that end in -teen;
is a kind of large integer

   The years of one's age having the termination -teen, beginning with thirteen and ending with nineteen; as, a girl in her teens. [1913 Webster]

teens, n.pl. the years of one's age from 13 to 19 (in one's teens).

N  youth, juvenility, juvenescence, juniority, infancy, babyhood, childhood, boyhood, girlhood, youthhood, incunabula, minority, nonage, teens, tender age, bloom, cradle, nursery, leading strings, pupilage, puberty, pucelage, prime of life, flower of life, springtide of life, seedtime of life, golden season of life, heyday of youth, school days, rising generation, young, youthful, juvenile, green, callow, budding, sappy, puisne, beardless, under age, in one's teens, in statu pupillari, younger, junior, hebetic, unfledged, youth on the prow and pleasure at the helm, youth a the glad season of life.