wallstreetcappers says:
It is a little complicated but I will try to explain.

The S&P and DOW has two contracts that are traded, the CASH contract and the FUTURES contract. The CASH contract is that which is currently active..so whatever the current contract in months..usually between 1-3 that is the CASH contract. The FUTURES contract is longer in duration, similar to the CASH but a contract OUT from the CASH.

So when they say "fair value" closing..it is how the CASH contract closes relative to the FUTURES contract..and if one is different, the other usually trades close to the other and corrects itself.

These futures contracts move the market and so that is why they talk about the SPX futures and the DOW futures.

It took me quite a while to understand it, but its just futures lingo and unless the difference is severe it wont mean much, plus the FUTURES trade all night long and that number can and will change.

The bulk of my above message is the "fair value" discussion, not the futures..