Topos Theory is a branch of mathematics that generalizes set theory and provides a framework for understanding different types of mathematical structures. It uses the concept of a category, which is a collection of objects and morphisms (arrows) between them, to explore relationships and properties in a more abstract way. In Topos Theory, a topos can be thought of as a category that behaves like the category of sets, allowing mathematicians to apply set-theoretic concepts in more generalized contexts. This theory has applications in various fields, including logic, geometry, and theoretical computer science.