According to Sports Illustrated's Jon Heyman via Twitter (copy is edited for better clarification):
"Jeter's contract very complicated. It's technically a four-year deal since he has player option in fourth year. Will get $51 million through three years if he declines."
"There's a point system for Jeter's contract. If he exercises fourth year he will get $56 to $68 million, depending on the points he earns. Points are based on winning MVP, finishing 2-6 in MVP, winning silver slugger and gold glove (a birthright award for him)."
Jack Curry of the YES Network tries to clear up the details of the contract on his blog.
"Jeter has a player option for $8 million in the fourth year, which could boost his guaranteed money to $56 million. In addition, Jeter has the chance to earn up to $9 million in incentives in the fourth year. The deal averages to $17 million for the first three years, which includes a $3 million buyout in the fourth year. If Jeter doesn’t exercise the $8 million option in 2014, he will make $51 million. If Jeter exercises the $8 million option, he loses the $3 million buyout and is guaranteed $56 million over the life of the contract."
So, there you go. The terms of the deal call for three seasons but Jeter has an option for a fourth.
Interesting that the deal calls for a point system based on winning postseason awards.
Again, it comes down to whatever make both sides happy.
With that said, it would have been very interesting to be a fly on the wall in the negotiating room. Especially, when they were trying to figure out the points system.