What is a closure in JavaScript?

A closure in JavaScript refers to a function that retains access to its lexical scope, even when the function is executed outside that lexical scope. This means that a closure can "remember" the environment in which it was created, including any variables or parameters that were in scope at the time.

For instance, when an inner function is defined within an outer function, the inner function forms a closure, allowing it to access variables declared in the outer function even after the outer function has completed its execution. This behavior is crucial for various programming patterns, such as data encapsulation and creating functions with private variables.

Understanding closures can help developers manage state and encapsulate functionality effectively, leading to cleaner and more maintainable code. Therefore, the correct answer highlights the essential characteristic of closures and illustrates an important concept in JavaScript's handling of functions and scope.