What is a 'tuple' in Python?

A 'tuple' in Python is defined as an immutable ordered collection of items. This means that once a tuple is created, its elements cannot be changed, added, or removed. The ordered aspect of a tuple means that the items maintain their position, allowing for easy retrieval based on their index.

Being immutable is a significant feature because it leads to more predictable behavior in programs. For instance, when you need to ensure that a set of values should not be modified throughout the execution of your code, using a tuple guarantees this. Additionally, tuples can be used as keys in dictionaries due to their immutability, while lists (which are mutable) cannot.

Overall, the characteristics of tuples—being both ordered and immutable—make them versatile for various programming scenarios where a stable grouping of values is required.