When a variable stores something (integer, string, etc) it’s actually storing a reference to the memory location where that thing is stored.

For mutable data types, lists for example, this can have interesting consequences. You can copy a reference to some variable, change the data within the actual data and it will be changed in both places.

>>> spam = [0, 1, 2, 3, 4, 5]
>>> cheese = spam # The reference is being copied, not the list.
>>> cheese[1] = 'Hello!' # This changes the list value.
>>> spam
[0, 'Hello!', 2, 3, 4, 5]
>>> cheese # The cheese variable refers to the same list
[0, 'Hello!', 2, 3, 4, 5]