Mutability, simply put: the contents of a mutable object can be changed, while the contents of an immutable object cannot.
All of the simple data types we covered first are immutable.
You can replace the value, but you can’t change it.
For the mutability of the container types we covered next, check this helpful list:
||ordered group of items, accessible by position||yes|
||mutable unordered group consisting only of immutable items. useful for set operations (membership, intersection, difference, etc)||yes|
||immutable collection containing ordered groups of items||no|
||contains key value pairs||yes|