To say that something was over the top awesome; to compliment someone on their awesome moments or themselves; The way of explaining uber-awesomeness (Adjective)
"Dude, you are Supertastical"
"That was a Supertastical Killionaire!"
"This is way Supertastical!"
When something is better than super and fantastic combined. Better than millions of flailing penguins. And when squiddles aren't a good enough measuring device for happiness. That's supertastic!