A monad is a design pattern used in functional programming to handle values and computations in a consistent way. Think of it as a container that holds a value and provides a set of rules for how to work with that value. This helps manage side effects, like input/output or state changes, while keeping the code clean and easy to understand. In programming languages like Haskell, monads allow developers to chain operations together without worrying about the underlying details. For example, the Maybe monad can represent a value that might be present or absent, making it easier to handle situations where data might be missing without causing errors.