Gran Turismo OmologatoThe name, which was DeLorean's idea, was inspired by the Ferrari 250 GTO, the successful race car.
It is an Italian abbreviation for Gran Turismo Omologato ("grand tourer homologated"), which means officially certified for racing in the grand tourer class.
"May the perfumes of the divine goddess embrace you as you slip off happily in a drunken dream!" ~ Guru
GTO in poker is an "absolutely perfect" strategy, one that cannot be beaten by any opponent regardless of their strategy.
The existence of such strategy has been proven by Nash a long time ago for any game (google Nash equilibrium), poker falls under that category.
Humans and computers haven't discovered the poker GTO yet, because the game is incredibly complex, but people apply some concepts into their game to improve their strategies and make themselves less exploitable.
Such concepts include having a balanced ratio of value to bluffs when betting, minimum defence frequency, correct bet sizing on different boards and a lot of other stuff.
That being said, "GTO play" often times isn't the one that makes you the most money against a particular opponent.
That's because people make mistakes, and in order to get the max value from them you have to adjust accordingly.
GTO, however, knows no adjustments - it only helps you to be less exploitable yourself.