What is the output of the expression ['Python', 'is', 'fun'][1]?

The output of the expression ['Python', 'is', 'fun'][1] is 'is' because the expression involves indexing into a list in Python. In Python, lists are zero-indexed, which means that the indexing starts at 0. Therefore, the first element of the list, 'Python', is at index 0, the second element, 'is', is at index 1, and the third element, 'fun', is at index 2. When you access the element at index 1 using the expression, it correctly retrieves 'is'.

The correct understanding of list indexing is crucial when working with Python, as it directly affects how we access elements and process data within lists.