The noun used to decribe the large heads of Ukrainians or their descendants. This is used comically by Ukrainians and other ethnic groups, especially in Canada. A Ukrainian trying on hats that all seem too small may curse his Ukrainium for being so huge. It comes from simply combining the words Ukrainian and Cranium. It's not intended to be or usually taken as a racial slur.

the thing that you don’t have when you’re phones percentage is over 20