
The symbolism behind Ellie's (Bella Ramsey) tattoo was finally unpacked in The Last of Us Season 2 Episode 6. Following a five-year time jump between Seasons 1 and 2, fans found Ellie as a 19-year-old, living in Jackson and sporting a large tattoo on her forearm. While this remains consistent with Ellie's character design in the game, HBO's TV show took the opportunity to spell out the meaning behind the unique design.
The tattoo's design shows a large moth perched atop a fern, which is large enough to cover Ellie's entire forearm. It also helps to hide the mutilated skin on Ellie's arm, which she self-inflicted (via chemicals in the game and by burning in the show), to cover up the infected bite mark she'd received years earlier.
What Does Ellie's Moth Tattoo Actually Mean in The Last of Us?

The Last of Us Season 2 establishes several things about Ellie's tattoo that were missing from Naughty Dog's The Last of Us Part II. While game players are left to draw their own conclusions about the meaning of the tattoo in the game, Episode 6 of the TV show lays it out for viewers.
The show establishes that Ellie's obsession with the moth design began as early as her 15th birthday. Joel (Pedro Pascal) is shown carving a moth emblem into the neck of a guitar, which he gifts Ellie for her birthday, saying he took inspiration from one of the moth drawings she'd hung on the wall.

Two years later, on Ellie's 17th birthday, she begins the tattooing process. Joel is initially angry that Ellie has gotten a tattoo, but later, he attempts to patch things up with his adoptive daughter by trying to understand the design. Ellie tries to dodge the question, saying she had read up about moths in a book and liked their symbolism:
Joel: "Never did ask, what is it with the moths?"
Ellie: "Nothing. I just read about them in a book on dreams and stuff. It's kind of symbolic."
Joel: "Oh, right. Like change and growing and such."
Still fixated on the tattoo's meaning, Joel goes to Jackson's resident therapist, Gail (Catherine O'Hara), to figure it out. He asks Gail what the meaning of moths is in dream theory, and she responds that they symbolize "death:"
Joel: "So a moth, that probably means change and growth?"
Gail: "No, that would be a butterfly."
Joel: "So what's a moth?"
Gail: "Death. If you believe in that sh*t."
What Ellie's Tattoo in The Last of Us Means For Her Character

Ellie's branding herself with an icon of death is symbolic of her character in several ways.
The most significant one is that Ellie was marked for death when she was bitten at 14. Her immunity took her and Joel on a trip across the country, where it was revealed that the Firefly surgeons would have to kill her to manufacture a cure for the cordyceps infection. But Joel's decision to save Ellie resulted in the death of all the Fireflies in the hospital, and it's haunted Ellie since (despite Joel's attempts to hide the truth from her).
The tattoo also plays into the idea that Ellie sees herself as a symbol of death, seeing as so many of the people around her have died: her mother, Riley, Tess, Sam and Henry, and then all the Fireflies at Salt Lake City. This is then flipped on its head in The Last of Us Season 2, as she becomes an active agent of death, killing many people in her mission for vengeance.
In an interview with the Washington Post around the release of The Last of Us Part II, creator Neil Druckmann said the moth was also intentionally similar to a firefly. The actions of moths constantly pursuing light, and that fireflies are a source of light (plus their motto is "look for the light") all tie together, as does Ellie's relentless pursuit of vengeance in the second game/season:
"There’s this idea of obsession and being drawn to a light and constantly pursuing this thing. And that’s how we got the idea as well for the loading screen, which is just moths being drawn to a light, which kind of looked like the spores [on the loading screen] in the first game. So, it felt like a sister image."
The tattoo also has greater meaning to Ellie following Joel's death in The Last of Us. Joel carved Ellie's moth symbol into her guitar, and the instrument became a point of connection between the two. With Ellie's tattoo also bearing the same moth as the one on her guitar, it constantly reminds her of her relationship with Joel.