Don’t ask Sutton Foster what “on fleek” means. She’s still not sure.

But she’s getting more accustomed to other trendy phrases and slang as the star of “Younger,” an original comedy series from “Sex and the City” creator Darren Star, which debuted on cable’s TVLand channel last year. The second season premieres Jan. 13.

Foster plays Liza, a woman returning to the job market after raising a family, only to discover she’s considered as outdated as the iPhone 5 because she’s . . . gulp . . . 40. With the help of pal Debi Mazar, she does a generation-gap makeover, reinventing herself as 20-something . . . and gets hired at a publishing company. Keeping up the charade becomes tricky as she finds new young friends (Hilary Duff) and romance (Nico Tortorella).

Before “Younger,” Foster, 40 herself, starred in ABC Family’s “Bunheads.” Before that, the actress-singer-dancer — yes, the original triple threat — has been a genuine Broadway sensation, appearing in 11 Broadway shows and winning two Tony Awards. Married to screenwriter Ted Griffin, she now lives in Los Angeles and New York, and recently chatted with Newsday contributor Joseph V. Amodio.

So how’s your transition going, from Broadway to TV?

It’s been a real learning curve, figuring out how to work in TV. It’s totally different from theater.

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Like stretching different muscles, I imagine.

Totally. And the idea of the audience is different. Onstage, the audience is right in front of you. But for TV you’re playing to an invisible audience behind a camera, so you have to change your idea about it.

How so?

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When I first started working in front of a camera, I was so used to performing to everyone — because onstage, everyone sees what you do. But in TV, instead of interacting with . . . [she puts on a grand theatrical voice] the entire THEATAHHH . . . you’re just interacting with one person behind the camera sitting in their home. I learned quickly I could be giving the performance of a lifetime but no one’s gonna see it if the camera is pointed at my back. (She chuckles.) That was a new concept.

Now that you’re faking 20-something, do you use phrases like “on fleek” with abandon?

Oh, God. I still don’t know what that means. It’s great to be educated about the 20-something world, though I’m not sure what’s rubbed off — I can’t say Liza’s style, because I couldn’t pull off her clothes. But . . . at least I understand more. Before, things would come up in the script and I’d think, “I have no idea what that is.”

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You wouldn’t get certain references?

Yeah. Like . . . “YOLO.”

The acronym? “You only live once”?

I’d have to Google it. But that’s what my character, Liza, does in the show, so I’m in good company. I turned 40 last March. It’s crazy. That thing happens where all of a sudden . . . you’re different. On New Year’s Eve, my husband and I went to a party and around 11:30 we were like [she whispers], “You ready? I’m ready. Let’s beat the traffic.” In one fell swoop we became . . . old. (She laughs.) But in my mind, I’m thinking, “It’s the sensible thing to do — beat the traffic, and celebrate at home with our dog.” I know, it barfs a little, but I wouldn’t have it any other way.

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In season one, I loved when you replied to a text with “Okay,” then deleted it, realizing that was so outdated — y’know, actually SPELLING — and texted “OK.” Then you deleted again — that’s so 10 years ago — and wrote “K” with an emoji. The generation gap used to be 20 years. Now it’s like . . . five minutes.

I know. Actually, I’m a fan of the emoji. When words fail, emojis are always there. Sometimes there’s no other way to reply than with a cutesy-faced emoji.

Much has been made of the show’s premise, and how similar it is to the plight of TV actresses — how tough it is to get roles once you hit 40. Have you worried you’ve come to TV too late? Or that you’re somehow playing catch-up?

I wasn’t pursuing television. I wanted to be onstage. And I was very lucky there. But my career’s unfolding . . . exactly as it’s supposed to. Oddly, the only time I felt pressure was when we premiered the first season of “Younger” and the press asked about ageism and getting older, and I thought . . . “Ohmygod, am I supposed to be panicking? I haven’t panicked yet.” But I’ve never felt that way. I don’t know if that makes me naive. But I’m gonna hold onto that naiveté as long as possible. So far, great opportunities have come my way. I’m actually excited to be a 40-year-old on TV. There are great roles out there for women, older and younger. I don’t need to be playing the ingénue forever.