teens

Age is measured the same way as the numbers: life enters the teens at thirteen and leaves them at twenty. The usual frame is in plus a possessive, as in in her teens or in his teens. The word stays plural even when it names a single stretch of a life.

The word is the shared ending turned into a noun. Thirteen through nineteen all end in -teen, while ten, eleven and twelve do not, so they stay outside the group. It is always plural and usually follows in when a count is rough rather than exact: the turnout was in the teens.

The countable plural, used for people: two teens, several teens, the teens next door. It shares its spelling with the plural-only teens of the teenage years, but here each teen is a person and can be counted. Older texts use teen for grief, sorrow or vexation. That archaic meaning has nothing to do with age, so do not read it into a modern sentence.

Naming decades this way follows the pattern of the twenties and thirties, but it fits this decade less neatly. That loose fit is why speakers also call it the tens or the oneties. The century is rarely stated, so context has to make clear whether the 1910s or the 2010s is meant. A speaker looking back on a recent pandemic plainly means the later one.

In weather reports and finance the word marks a band of values rather than a count. Temperatures drop into the teens and rates climb into the teens, and the unit goes unsaid because context supplies it. Unlike the counting sense, this band begins at ten, so a reading of 11 or 12 still falls within it.