What is a key difference between a list and a tuple in Python?

The key difference between a list and a tuple in Python is that a list is mutable while a tuple is immutable. This means that once a tuple is created, its elements cannot be changed, added, or removed. In contrast, lists allow for modification after creation, which includes altering elements, appending new elements, or removing existing ones.

This distinction is crucial in programming because it affects how the data structure can be used; for instance, tuples are often used for data that should not change throughout the program's lifecycle, while lists are suitable for collections of items that may need to be modified. The immutability of tuples can also lead to performance benefits, as they can be optimized by Python in ways that mutable structures cannot be.

Regarding the other options, lists do have the capability to hold multiple data types, just like tuples. Additionally, the speed of processing can vary depending on the context, but it isn't a definitive characteristic that distinguishes lists from tuples. Finally, tuples are not typically considered more flexible than lists because their immutability restricts their ability to be modified, which is a key aspect of flexibility in programming.