What are closures?

Closures are a programming concept where a function retains access to variables from its lexical scope, even after that function has finished executing. This allows the function to remember and use those variables when it is invoked later.

In simpler terms, a closure is a function that captures the environment in which it was created, including any local variables or parameters that were in scope at that time.

Example in Python:

```python

def outer_function(x):

    def inner_function(y):

        return x + y

    return inner_function

closure = outer_function(10)

print(closure(5))  # Output: 15

```

In this example, `inner_function` forms a closure that retains access to `x` from `outer_function` even after `outer_function` has finished executing.

Closures refer to a programming language feature where a function can access and use variables declared outside of its own scope, even after the parent function has finished executing. In essence, a closure "closes over" or captures the lexical environment (scope) in which it was created, allowing it to retain access to variables, parameters, and even outer functions.

This capability is particularly useful in functional programming and languages like JavaScript, where closures enable powerful and flexible patterns such as function factories, private variables, and callbacks that maintain access to their originating context.