A keloid is a "thick scar resulting from excessive growth of fibrous tissue" (
http://www.fasthealth.com/dictionary/k/keloid.php).
I have an innie. It's cute and I have gotten several compliments on it.
My boyfriend has a cavernous innie...I can fit my forefinger inside of it up to the second knuckle! I stick my finger in his belly button all the time just to piss him off because he hates that his innie is so freakishly deep.
