OK, having read the rules I have come to the following conclusion:
Contest = one attacking dice roll versus one defending dice roll = Attacker Contest Roll versus Defender Contest Roll
Let me cite the book:
Page 13: The Contest Roll
"Contests are resolved through contested dice rolls. Both players involved in a contest roll a specific number of dice (determined through various in-game factors) and compare their results. The player with the most successful die rolls (see blow) wins the Contest. This is referred to as the contest roll."
Page 15: Campaigns - Outcome of a Campaign Contest
"In a subsequent turn, the attacker may use a military action to continue his campaign and fight another contest in the province."
Page 16: Sieges - Outcome of a Siege Contest Roll
"At the end of the siege contest, the attacker chooses whether he wants to stop the siege and retreat to the province his army previously occupied. If he does so, he immediately moves his army back to that province. If he does not, the two players fight another siege contest. Successive contests continue until the attacker decides to retreat... etc."
Page 17: Battles - Outcome of a Battle Contest Roll
"If neither side retreats, new battle contests are fought until one combatant decides to retreat, or one army is completely removed."
This is my interpretation of the rules. I have highlighted the specific wording that makes me believe that a contest equals two opposing die rolls