Explain what is meant by the term 'closure' in programming.

Closure is a function that remembers and can use variables from an outer scope even after the outer function has finished executing.

Example in Python:

def outer(x):
    def inner(y):
        return x + y  # inner uses variable x from outer
    return inner

f = outer(10)
print(f(5))  # Outputs 15

Here, inner is a closure that "captures" the variable x from the outer function and retains its value even after outer has completed.