Which of the following is NOT a built-in data type in Python?

The choice of "Buffer" as the answer is correct because it is not considered a built-in data type in Python in the same way that the others are. Python has several built-in data types that are fundamental to programming in the language, including lists, sets, and tuples.

A list is an ordered collection that can hold a variety of items, including other lists, and allows for modification of its contents. A set is a collection of unique elements, meaning there can be no duplicates, and it is unordered. A tuple is similar to a list but is immutable, meaning once it is created, its content cannot be changed.

While Python does include a bytes type that represents binary data, the term "buffer" is not specifically recognized as a standard built-in data type in Python. Therefore, it stands out among the options as the one that does not belong in the same category as list, set, and tuple.