It called Tenet because it's a palindrome and it will take ten viewings or ten years of continuous viewings to understand

A palindrome is a word, number, phrase, or other sequence of characters which reads the same backward as forward.

Tenet is an extremely confusing and complicated movie and depending on a person's intelligence quotient (IQ), it'll either take ten viewings or ten years of continuous viewings to understand it without searching for any Tenet help videos on YouTube.

Tenet is a very clever, complex and puzzling experience, it's the most convoluted movie I have ever watched. Even though I was so confused, I loved it both times I've watched it. Only 8 more viewings or approximately 9.5 years of continuous viewings to go before I understand this mind bending masterpiece....