The best possible example of something.
A Platonic ideal.
To be of discernibly higher quality than all other related things.
The film Citizen Kane, said to be the preeminent form of filmic endeavors, and it's subsequent invocation in describing the quality of other things.
"Dude, that play in this sports match we are watching was kane!"
"Did you see that crazy kaner punch that bear in the face?! That bear didn't stand a chance!"
"Half-Life is the kanest game ever made."