What does the `len()` function return when applied to a list?

The len() function is a built-in Python function designed to return the number of items contained within an object. When applied to a list, it specifically counts and returns the total number of elements in that list. This capability allows programmers to quickly determine the size of the list, making it a fundamental function for managing collections of data in Python.

For instance, if you have a list defined as my_list = [1, 2, 3, 4, 5], using len(my_list) would yield the result 5, which signifies that there are five items in the list. This utility is essential for various operations, such as iterating over the list, checking if it is empty, or performing conditional logic based on the list's size.