Special items and extraordinary items may sound similar and their definition may be very close to one another, but in fact they are different. Let us define special items first. Special items are those that are unusual OR infrequent (but not both). On the other hand extraordinary items are those that are both unusual AND infrequent. This "OR", "AND" can make a world of difference in determining the nature of the event, its significance and the method in which it should be recognized.
In understanding the above definitions and the differences between the two types of items, it is noteworthy to mention that an extraordinary item is ALWAYS special; while a special item is NEVER extraordinary.