An ordered pair is a pair of mathematical objects for which the order of those objects is significant.
For objects 
and 
, the ordered pair with as the first element and as the second is denoted: 
.
Since the order is important, 
= 
if and only if 
and 
. This also means that the ordered pair is only equal to its reverse, 
, when 
.
This enforced order is one way in which ordered pairs are different from sets, whose order does not matter. ie., 
.