How does a closure maintain access to variables in its outer scope even after the outer function has returned?

<!-- BEGIN COPY / PASTE -->
        function outerFunction() {
            let outerVariable = "I'm outside!";
            
            function innerFunction() {
                console.log(outerVariable);
            }
            
            return innerFunction;
        }

        const closureExample = outerFunction();
        closureExample(); // Logs: "I'm outside!"
        <!-- END COPY / PASTE -->