A kōan is a very short story intended to provoke thought and contemplation for students of Zen Buddhism.
A hacker koan is an appropriation of this idea into hacker folklore, using the medium to express computing wisdom.
It might be better if you read actual Zen kōan first but here are a few classics:
@erkin those are great, thank you
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko