It is a great pity that everybody else has failed to speak of ko intersections but makes things more difficult by immediately jumping into the more abstract cycles. The page was said to be an introduction, so why not start with introductory contents (a description of what is visible on the board)?

As long as I am researching in a formal and general definition of "ko intersection", the following informal explanation will do: The ko intersections are the intersections of that a ko consists, where meaningfully recurring stones might be played and removed.