# Contour set in Mas-Collel, Winston and Green

Mas-Colell, Winston and Green's Microeconomic Theory uses the notion of contour set, as shown hereunder:

In the context of Microeconomic Theory, what would be the definition of a contour set?

The upper contour set is $$UC(x)=\{ y|y \succsim x \}$$, i.e., all the goods baskets that are at least as desirable as $$x$$. Similarly, the lower contour set is $$LC(x)=\{ y|x \succsim y \}$$, i.e., all the goods baskets that are at most as desirable as $$x$$.