'Stranger Things' Star Millie Bobby Brown Reveals Her Biggest Fears, Talks New Friendship With Maddie Ziegler

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Plus, the 12-year-old actress reunites with co-star Winona Ryder at NYFW.

Millie Bobby Brown gave Stephen Colbert a lesson on the trendy slang used by millennials.

The 12-year-old Stranger Things star was a guest on The Late Show on Tuesday (the youngest guest he's ever had, in fact), and during her interview with the host, she grilled him on Twitter, hashtags and the true meaning of bae.

WATCH: In Defense of… Barb!

It all started when Brown explained that she and her new bestie, former Dance Moms star Maddie Ziegler, have created their very own squad -- and if you want in, you must pass their friendship test!

"Me and Maddie are taking castings now," the Spanish-born, English actress joked. "Let's go with the test, shall we? What does bae mean?"

"Bae? It's your sweetie," Colbert replied. "Like your special one. Bae-by."

Brown revealed that he was wrong, telling him it stands for "before anyone else," before moving on to her next question: "What does lit mean?"

NEWS: Aaron Paul and His Wife Have Officially Succeeded in Adopting Eleven From 'Stranger Things'

"Want me to give you an example?" she asked. "This interview is lit."

"Oh, it's super cool, it's happening," Colbert exclaimed.

"It means it's just raving," she said, correcting him. Watch the video below to hear more.

Although Colbert didn't exactly pass Brown's test, he was able to get her to talk about the cult-like reaction the '80s-inspired Netflix show she stars in has received since its July debut.

NEWS: Millie Bobby Brown Shares Video of Herself Getting Buzz Cut to Play Eleven

"It's been a four-year, overnight success," Brown explained of her rise to stardom. "I started [acting] when I was around eight. It's very overwhelming in the best possible way. It's all very new, and it's fantastic."

To prepare for her role as Eleven, Brown told Colbert her "research" was mostly asking her parents a lot of questions.

"It wasn't who, it was [more] like what is that, you know? Like I didn't know what a record player was," she admitted, also telling Colbert her parents bought her one for Christmas. "I love Adele, I love Ed Sheeran and Amy Winehouse, Beyoncé. I got the vinyl set and I was like, 'This is my life now.'"

Brown, who admitted she "couldn't say Demogorgon at first," also revealed that she, too, sometimes gets spooked by the show -- and a lot of other "things in general."

RELATED: Millie Bobby Brown Can Incredibly Rap the Whole Nicki Minaj 'Monster' Verse

"Oh, it does [scare me], I'm frightened about everything," she explained. "Sharks, the dark, bungalows -- bungalows really freak me out. It's a house with no stairs. [What's scary is] you have no place to escape. You're on one level."

During another point of the show, Brown reprised her role as Eleven, with Colbert portraying Dr. Martin Brenner. "Alright Eleven, it's time to do what we discussed," the 52-year-old talk show host said in the clip. "There's no need to be afraid, just stay focused."

Brown then used her powers to cook a burrito in a microwave, popping open the door and having it magically make its way in front of Colbert's place on the table. See it all go down in the video below.

NEWS: 'Stranger Things' Officially Confirmed for Season Two!

While in the Big Apple, Brown also got to attend New York Fashion Week for the first time, reuniting with her Stranger Things co-star, Winona Ryder, front row at the Coach 1941 Women's Spring 2017 runway show. Brown wore a blush pink bomber jacket over a printed dress, while Ryder sported a black Coach sweater emblazoned with a green and brown T. rex.

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"Reunited at last," Brown later wrote on Instagram, using the hashtags, "#strangerthings" #netflix" "#joyce" and "#eleven."

WATCH: Joe Keery Talks 'Stranger Things' Season 3, Steve's Hair and Justice for Barb

Last month, Netflix announced Stranger Things is officially receiving a second season. Ahead of the exciting news, ET caught up with Brown and Ryder's co-star, Joe Keery, who shared his hopes for his character, Steve Harrington, and why he wants "Justice for Barb."

Hear more in the video below.