"One" has many debated meanings. The ambiguity is likely the main aspect that popularizes the song, allowing for many different interpretations. There are 3 video versions to the song which add to the discussions. One of them suggests that it's about a gay son confessing to his father that he is HIV-positive—largely assumed because of the content of the third video, directed by Anton Corbijn, in which Bono (dressed in drag) sings the song to his own father. It is filmed in Berlin and has footage of the band driving in Trabant cars. Also, a large amount of sales from the single went to AIDS charities. The first version has footage of blooming flowers and buffalos, interspersed with numerous black title cards featuring the word "one" in white lettering, depicted in numerous languages. The buffaloes in the video originate from a photo by David Wojnarowicz, a gay artist who died of AIDS. The photo is on the cover of the single. Yet another version of the video shows Bono in a bar, smoking a cheroot and drinking beer.
The most basic interpretation suggests the song to be about two people who love each other, but hurt each other too much to continue with their relationship, which is a prominent lyrical theme. The Edge in Q magazine said, "I often come across people who've told me they played it at their wedding, And I think, 'Have you listened to the lyrics? It's not that kind of a song'". Others interpret the song as achieving oneness in the spiritual sense, while yet another point of view suggests that it's about the reunification of East and West Germany and the subsequent, slow healing of past wounds as the Berlin Wall collapses. This particular one is popular due to the time the band spent in Germany during the album's creation.
However, the most popular interpretation suggests that the song is about Bono's lifelong relationship with his father, based on their shared experiences following the death of Bono's mother when he was 14.