What is the difference of two sets? Provide an example.

The difference of two sets is about finding what items are unique to the first group when compared to a second group. You take items from the first group and try to pair them up, one by one, with items from the second group. The items in the first group that do not find a pair are the difference.

For example:
Imagine you have a group of animals: Set A = {cat, dog, bird}.
And another group of animals: Set B = {cat, dog}.
To find the difference (A - B), you match the 'cat' from Set A with the 'cat' from Set B, and the 'dog' from Set A with the 'dog' from Set B.
The 'bird' in Set A has no match in Set B.
So, the difference is {bird}.