A closure is a function that retains access to its outer scope's variables even after the outer scope has finished execution.
This allows the function to 'close over' its surrounding state, preserving the state of the outer scope at the time the closure was created.
Closures are commonly used to create private variables and methods in JavaScript, as they provide a way to encapsulate state within a function.
They are also used in event handlers and callbacks, where they allow functions to maintain access to their original context.
Closures are created every time a function is defined in another function, and they have access to the variables of the outer function even after the outer function has returned.
Understanding closures is important for writing clean and efficient JavaScript code, as they are a powerful feature of the language.