Very, very big or huge.
Superlarge things are so big that they can be surprising or hard to believe.
Examples:
The elephant is superlarge.
I saw a superlarge cake at the party.
The superlarge truck took up two parking spaces.
The superlarge pizza was as big as the table!
The superlarge mountain reached up to the sky.
The superlarge balloon was as big as a house.