"Seven" is a song by the American singer-songwriter Taylor Swift from her eighth studio album, Folklore (2020). Swift co-wrote the song with its producer, Aaron Dessner. "Seven" is a folk song with nostalgic lyricism. It blends present and past perspectives: 30-year-old Swift reflecting on her childhood in Pennsylvania while recalling the purity of her relationship with an old friend and the then 7-year-old narrator incapable of understanding the domestic violence her friend had experienced but realizing it years later. The song is led by Swift's upper register over a swirling piano line, complemented by acoustic guitars, drums, and strings.

The song garnered positive reviews from music critics, many of whom chose it as a standout on Folklore as it dealt with a sensitive topic like child abuse. They also highlighted the experimental composition and Swift's upper-register vocals. Following the release of Folklore, "Seven" debuted at number 35 on the Billboard Hot 100, number 11 on the Rolling Stone Top 100, and number 7 on the US Hot Rock & Alternative Songs. It also reached the top 30 in Australia, Canada, Malaysia, and Singapore.

Swift conceived all the tracks of her eight studio album, Folklore, as imageries and visuals from her deep subconscious, a result of her imagination "running wild" while isolating herself during the COVID-19 pandemic. "Seven" was the second song that Swift and her co-writer and producer, Aaron Dessner, wrote for the album, following "Cardigan". Dessner recalled that "Cardigan" and "Seven" laid out the roadmap for writing the rest of the album. He classified the song as "wistful and nostalgic". Describing the writing process as "looking back at childhood and those childhood feelings, recounting memories and memorializing them," he identified the lyric "And just like a folk song, our love will be passed on" as a defining moment of Folklore, commemorating friendship and nostalgia.

Folklore was released on July 24, 2020. It featured "Seven" as the seventh song in the track-list. In the primer that preceded the release, Swift teased various tracks, with "Seven" being about "the tree swing in the woods of my childhood. Hushed tones of 'let's run away' and never doing it." Lyric videos of each song on the album were released to Swift's YouTube channel; "Seven" has since garnered over 21 million views as of August 2024. The song was also included in Folklore: The Escapism Chapter and Folklore: The Saltbox House Chapter, streaming compilations by Swift released on August 21 and August 27, 2020, respectively. Commercially, "Seven" debuted at number 35 on the Billboard Hot 100 chart alongside the album's 15 other songs and at number 11 on the Rolling Stone Top 100. Additionally, the song debuted at number seven on the Billboard Hot Rock & Alternative Songs chart. The song reached the top 20 in Australia, Malaysia, and Singapore.

"Seven" is played during the closing credits of the 2022 coming-of-age drama film Summering. The song is played in the final episode of the second season of British coming-of-age television series Heartstopper. From March 2023 until March 2024, snippets of "Seven" were included on The Eras Tour (2023–2024) as a spoken interlude before the Folklore set. At the tour's second show in Pittsburgh, she performed a full version of the song with Aaron Dessner on piano as one of the show's two surprise songs, which are songs that are not part of the set-list that Swift decides to perform during the acoustic set of the show. Swift dedicated the performance to her dad in honor of Father's Day, saying "This song has to do with really fond memories of childhood and growing up in Pennsylvania."

"Seven" is a nostalgic and "wistful" folk song presenting "the pureness of childhood friendship" from the perspective of a seven-year-old Swift, who is unable to comprehend the emotional and physical abuse of her friend from their parents. The song also describes young Swift's naive efforts to help her friend's escape from the abusive household, and run away to India. The song switches between the use of past and present tense. The song hints at her witness of the abuse and her inability to stop it in lyrics such as: "And I've been meaning to tell you / I think your house is haunted / Your dad is always mad and that must be why / And I think you should come live with me / And we can be pirates".

Several lines also see Swift "pay tribute" to the innocence of her infancy as per The Independent's Roisin O'Connor, reminiscing the purity of her relationship with her friend, whom she cannot fully remember. Rebecca Karpen of PopMatters compared the themes of childhood nostalgia and the inevitability of growing up to her songs "Stay Beautiful" and "Mary's Song (Oh My My My)" from her self-titled debut album (2006), "The Best Day" from Fearless (2008), "Never Grow Up" from Speak Now (2010), and her 2012 charity single "Ronan". Eric Mason of Slate highlighted the song's summer imagery, comparing it to that of "August" and "Betty". The lyric "Or hide in the closet" also possibly alludes to her friend's potential homosexuality, according to the critics from Insider and The Advocate.

Musically, the song is set in the key of E major with a tempo of 95 beats per minute. Swift uses her upper register, and her vocals span from E₃ to B₄. The song is instrumented by a prominent piano composition in conjunction with acoustic guitar, drums, cello, viola, and violin. Its melody mimics the movement of a pendulum, elongating at its high point before rushing down and rising up again.