What does this represent?

(Thing 1) I, at the start, am old Many centuries I've been told Used by the Greeks For counting techniques After things were bought and sold

Later is when I became known As an infinite figure, when shown You've counted my spaces Over two billion places And still, my amount is unknown

(Thing 2) I, too, am not young I'm almost as old as Thing 1 I'm just a frog On the natural log But I can make counting fun

(Thing 1 and Thing 2) When you combine us two In the order of Thing 1 and Thing 2 We'll be a baked treat That's painful to beat Whether cherry, peach, or aloo

Thing 1 is "Pi."

Thing 2 is "e," the base of the natural logarithm.

Thing 1 and 2 are, together, "Pie."

(an aloo pie is a potato pie)