In anime, a "glow-up" is when a character becomes greatly enhanced on the inside, the outside or both. Glow-ups might occur after a time skip, for example, or if the character vanishes from the narrative early on and reappears later with new superpowers, a new outfit, newfound confidence and more. The Naruto anime did this, too.
The Naruto anime is famed for its two-and-a-half-year time skip between the original series and the lengthy Naruto Shippuden, with the Konoha 11 members going from tweens to more grown-up adolescent ninjas with new outfits, new jutsu, more mature personalities and more. A few key Naruto protagonists returned better than ever when Shippuden started, while others merely had cosmetic glow-ups to try and keep pace with the real heroes.
When Naruto's Main Heroes Got Meaningful Glow-Ups in Shippuden
When Naruto Shippuden began, protagonist Naruto Uzumaki finally returned to the Hidden Leaf Village after two years of grueling training with his best mentor, Jiraiya the toad sage. Most importantly, Naruto was clearly an older, stronger and wiser young man than ever, but without sacrificing any of the essentials that made him who he is. He was still a cheerful bakadere who loved and supported everyone around him, and he was still a prankster who dreamed of becoming Hokage. However, he was also taller and more imposing, and with greatly enhanced combat techniques and strategies to match. During his second bell training exercise with Kakashi Hatake, for example, Naruto actually outmaneuvered Kakashi at first -- a total reversal of how Kakashi easily restrained Naruto when the first test began. Naruto also had a cool new outfit and a slightly more mature and grounded personality.
Similarly, Naruto's remaining teammate Sakura Haruno had an impressive glow-up when Shippuden began, even if she plateaued too early in the series. When Naruto met her again, Sakura was not just older and more beautiful but also far more confident as a capable, hard-hitting kunoichi who could finally take pride in herself and her abilities. It was a major step forward in Sakura's arc; a personal journey of self-actualization that began in Sakura's girlhood with her oversized forehead. Early in Shippuden, Sakura wowed everyone with her chakra-infused punches -- something she learned from Tsunade -- and her advanced medical jutsu that saved Kankuro's life. Sakura didn't have a hiden jutsu or kekkei genkai, but she did have her own "thing," giving her character far more definition than just her infatuation with Sasuke.
Similarly, the dandere Hinata Hyuga and the redeemed Gaara of the Sand hit the ground running with impressive glow-ups in Shippuden, though the payoff was different. Gaara's glow-up was purely internal, with him attaining the rank of Kazekage and fighting valiantly to defend not himself but the entire Hidden Sand Village and everyone in it. Gaara had a noble cause to fight for at last, and the responsibility made him humbler, wiser and stronger. Meanwhile, Hinata had an outward glow-up where she became a charming, soft-spoken beauty, and by then, her fighting style had been revamped as well. Hinata didn't show it right away, but she had become a truly powerful, bold kunoichi who could fight by Neji's side as a mighty Hyuga warrior and take on any foe. Hinata's glow-up paid off the most when she stood between Naruto and Pain as a brave and strong kunoichi in love.
When Shippuden Dished Out Cosmetic Glow-Ups to Keep Everyone Even
The rest of the Konoha 11 got glow-ups too, but mostly on a cosmetic level. If the main characters were older and had new outfits and new jutsu, then the narrative needed everyone to get those glow-ups, or it would look odd. Superficially, Naruto Shippuden made sure no one got left behind with their glow-ups, but it was still unequal by necessity. By then, Naruto's cast of characters was too large for everyone to truly shine or reinvent themselves, so other Konoha 11 characters just got mild, straightforward boosts in their appearance and jutsu. On the inside, they didn't change very much, as their character arcs would either be expanded upon later or not really change at all.
Shino Aburame, for example, was the same bug-loving kuudere as ever, just with a new hooded outfit and stronger jutsu, along with his chunin rank. The same was true of Neji Hyuga, who obtained a new outfit and the jonin rank without changing much otherwise. Choji, Tenten, Kiba and Rock Lee were the same way, and up to a point, so was Shikamaru Nara -- although at least the latter grew up later and changed when Asuma Sarutobi died and Shikamaru started emulating him more than ever.
This proves that with glow-ups, any shonen anime must be choosy because it can only allocate so many meaningful glow-ups. The main heroes are due for the biggest changes since they're the main draw, and side characters only incrementally evolve so that the series doesn't look too uneven. Such was the case in Naruto Shippuden, and in hindsight, it worked wonderfully.