"Seasoning is the coating of polymerized oil and fat that covers the iron and gives it the characteristic black color. (Raw cast iron is gray, not black.)"
If you've got a nasty, sticky layer of polymerized oil on your cast iron, you're a couple of days away from a RANCID layer of nasty, sticky polymerized oil on your cast iron.
A properly seasoned cast iron pan will be black, but it will be glossy and smooth and hard.
A proper seasoning layer beings with oil or grease, which is then heated to the point where the oil molecules being to unravel. The hydrogen atoms burn off in the form of smoke, leaving a thin layer of carbon atoms behind. It's that layer of carbon atoms that provides the magical non-stick qualities to cast iron (or, for that matter, any steel).
That layer of carbon atoms is amazingly durable. It can withstand soap and hot water, it can withstand long, low simmers of tomato sauce or other acidic foods, it can stand boiling a soup or stew for hours. It can even withstand light abrasion from metal utensils.
What it can't stand, though, is high heat in an empty, dry pan. That will burn the carbon layer off, leaving you with raw, unseasoned cast iron.
