I wonder what the principal ways of (direct) cortico-cortical connections are.
I came up with the following possibilities:
vertical: a cortical neuron connects to another one in roughly the same cortical column, but in another layer
horizontal: a cortical neuron connects to another nearby one, preferably in the same or neighboring layer
"intragyric": a cortical neuron connects to another one in the same gyrus (see here)
interhemispheric: a cortical neuron connects to another one in the same (or neighboring) area of the opposite hemisphere
Are all of these relevant? And/or are there relevant but completely different ways of cortico-cortical connections, e.g. "intergyric"?
Addendum: Maybe too late I found a concise summary in the Wikipedia articles on white matter and association fibers (the latter term I wasn't aware of when I asked my question), which doesn't contradict and complements Bryan's answer:
intracortical (Bryan: "intracolumnar" vs. "horizontal")
short association fibers ("also called arcuate or U-fibers [...] connect together adjacent gyri")
long association fibers which "connect the more widely separated gyri and are grouped into bundles" (often called fasciculi, but probably not exclusively)
commissural fibers (Bryan: "callosal projections")
There definitely seems to be no reserved name for something like "intragyric" fibers (see second addendum here).