When a pair
of numbers such as (2,3) is represented as a point on graph paper,
then the order of the numbers is important.

In this case the first
number 2, is the x-coordinate and the second number, 3, is the
y-coordinate. See point P. The pair (3, 2) is represented by Q whose
x-coordinate is 3 and y-coordinate. When the order of two numbers
is taken into account they form an ordered pair.

In contrast, consider
a game where someone wants to score a total of 5 from the roll of
two dice. It makes no difference whether a 2 follows a 3 or a 3
follows a 2.