What is CellId and What Is It's Use?

I have came across (something I think is a UserData) CellId. It has a constructor like BrickColor and Vector3 and etc. However, I don't understand what it means.

This is what I have got in the output.

print(CellId.new())

{false}, {2.91794061e-39, 0, 0}

print(CellId.new(true))

{true}, {2.91794061e-39, 4.34070528e-38, 0}

CellId.new() seems to return two tables. There are also optional arguments(from what I see) new is the only thing I could find in the CellId table

I couldn't find any documentation on this UserData. I hope I can find some information on this.