In mathematics, ahe oximation is used to establish a numerical representation of something that's nearly impossible to be exactly accurate at.
We have the number of bluebirds in the United States, it's pretty unlikely to know the exact total number of bluebirds around the U.S.
The amount of money you owe in loans is typically not approximated because it's a decimal number that we approximate.
The number of leaves on a tree is typically approximated because you don't count leave-by-leave to find it.
The distance from New York to Beijing is typically approximated because you don't directly measure that distance around the globe.