the time of life between the ages of 12 and 20
"During my teens, I spent more time hanging out with friends than studying for exams."
all the numbers that end in -teen
"The teacher told us to circle every number from 13 through 19, which are the only ones containing the word teens."
plural of teen
"The school dance was a huge success for all the teens in attendance."
In plain English: Teens are people who are between the ages of thirteen and nineteen.
"My son is in his teens now."
The word teens comes directly from the Old English suffix used for numbers ending in ten, such as thir-ten and four-ten. It entered modern usage simply by dropping the initial number names while keeping the "-teen" sound that originally meant "ten.