The act of fully inserting one's cranium into a women's vagina and ideally crawling into her womb. It is the reverse of the birthing process, specifically crowning. It is advisable to cover one's head in a balloon of some sort in order to maximizepleasure.
Someone that crooms a lot is considered a 'croomer'.
Charlene : I was so depressed that I croomed during breakup sex.
Gabriel : I get that, last night was so good except she reminded me of my dead mom. I was crooming a little.