An algebraic stack is a mathematical structure that generalizes the concept of a scheme in algebraic geometry. It allows for the study of moduli problems, which involve classifying geometric objects, such as curves or surfaces, up to certain equivalences. Algebraic stacks can handle situations where objects have non-trivial automorphisms, making them useful for more complex scenarios than traditional schemes. These stacks are built using categories and functors, incorporating ideas from both algebraic geometry and category theory. They provide a framework for understanding families of algebraic objects and their relationships, often represented through objects like sheaves and morphisms. This makes algebraic stacks a powerful tool in modern mathematics.