Actual responses to actual questions from students of Math 344, Introduction to Combinatorics (Spring 2004).
The book asks to list all nonisomorphic undirected graphs with 4 vertices. Does this mean to list all pairs of graphs (where both graphs have 4 vertices) that are nonisomorphic?
No, this means to produce a list undirected graphs any pair of which are not isomorphic. (So any two of them from the list are nonisomorphic.)
To give you an example in fruit, pairs of nonisomorphic fruit would be things like
(apple, banana) or (apple, grape) or (apple, kumquat).
That's not what we want; we want a list
{apple, banana, grape, kumquat,...}.