The Tenet ending reveals the true meaning of the film's title, and provides clarity about the main protagonists' motivations. Due to the complex time travel premise, however, some viewers may remain unclear about the movie's specifics, and how the final battle at Stalsk-12 in Northern Siberia affects the in-universe timeline. In short, the word "Tenet" derives from the climactic mission in which two CIA squads execute a "temporal pincer movement" and have 10 minutes to achieve their goal.
Prior to Tenet's wide release in September 2020, the palindromic title and cryptic trailer naturally sparked numerous theories about the film. For example, Hayley Atwell narrated a video about the Sator Square, a palindrome that was originally found in the ruins at Pompeii, and includes the words SATOR, AREPO, TENET, OPERA, and ROTAS. In Christopher Nolan's film, he uses the Sator Square as the structural foundation for the story. He informs audiences that "Tenet" has several meanings, and he associates the rest of the Sator Square words with specific characters for narrative symmetry.
In Tenet, a CIA agent known only as Protagonist (John David Washington) survives a failed mission at the Kyiv opera house. He subsequently s a secret organization called Tenet, and learns that someone has produced bullets that invert backwards through time. Protagonist tracks them to Russian businessman Andrei Sator (Robert Pattinson), though, Protagonist receives clarity about the real meaning of "Tenet" - it's a time-sensitive inversion operation that's part of larger plan.
Tenet divides into two teams to execute a "temporal pincer movement" that will allow them to acquire the algorithm. Specifically, they need it to prevent Sator from wiping out humanity so that a future generation can inverse and escape an uninhabitable Earth ("their oceans rose and their rivers ran dry"). Over the course of one hour, a red team moves forward in time while a blue team inverses. Conceptually, this will give them a 10-minute timeframe to share logistical intelligence. Protagonist is part of splinter red team with Commander Ives (Aaron Taylor-Johnson), while Neil inverses with the blue squad. The Tenet leaders eventually acquire the algorithm, while Kat inverses back in time to kill Sator in Vietnam. Tenet ends with Neil inversing to help the splinter agents, only to reveal that he's going to inverse once again to pick a lock and save Protagonist's life during the 10-minute mission.
Ultimately, the 10-minute mission in Tenet is symbolic of the film's overall structure. As Protagonist moves forward towards his destiny (founding Tenet in the future), Neil inverses backward to ensure that his mentor is protected. Pattinson's character provides clarity during the final moments by explaining that the entire mission has been a temporal pincer, and that they've now reached the middle. Neil also tells Protagonist that he'll see him "at the beginning," which makes Tenet even more complex when considering that Kat's son is most likely a younger version of Neil.
