Is TERNS a Wordle Word?

Yes. TERNS is a valid Wordle word.

It is not on the Wordle answer list, so it is unlikely to be a daily answer.

Plurals ending in S are almost never chosen as Wordle answers.

What does TERNS mean?

/ˈtɜː(ɹ)nz/

Any of various sea birds of the family Sternidae that are similar to gulls but are smaller and have a forked tail.

That which consists of, or pertains to, three things or numbers together.
A lottery prize resulting from the favourable combination of three numbers in the draw.

Definition from Wiktionary, available under the CC BY-SA license.

Starter word rating: GoodIn the top 3% of all valid Wordle words for testing common letters.
Vowels: E
Unique letters: 5 of 5
Common letters: T, E, R

Hard-mode trap: 6 valid words fit the pattern _ERNS. If you reach it, you may need several guesses to find the last letter.

Letter ratings use how often each letter appears in Wordle answers.

Tap its tiles to the colours Wordle showed, and the Wordle Solver lists every word that still fits, with the best next guess.