A blackout date is a date that a wholesaler can't sell any rooms.
If ABC Travel has a contract with a hotel for 20 rooms a night at rate X, the hotel puts in a block of 20 rooms under that company's name. ABC travel has a cutoff time (3 days, 7 days, or something like that) to get the names of the rooms they sold to the hotel. And if they don't sell all 20 there's probably no penalty, depending on how their contract is set up with the hotel. This is why sold out dates can open up at the last minute; when groups don't fill their blocks the rooms get released back into inventory to sell. And this is why your hotel may not have your ressie in its system when you make it with the wholesaler; the ressie is there, just under the company's name and not yours, until they get the names over to the hotel.
However, let's say that for certain dates (New Years Eve, Super Bowl, Spring Break, etc.) the hotel can sell all its rooms at a higher rate and doesn't need help from its wholesalers. They tell the wholesalers, these dates are blackout dates; i.e., dates where their block is 0 or maybe a very limited number. Sometimes the wholesalers are told up front what these dates are and sometimes they are told peridocally throughout the year, i.e., we are "stop selling" date such and such and they'll accept what is currently sold and not accept any new reservations. It sound like the reservation in question was for a blackout date and Expedia didn't figure it out soon enough.
Not sure what a ghost room is, unless it's a reservation that's part of the block without a name attached to it yet.
I just don't trust these booking engines at all. Have seen too many cases of people losing their money on cruises, vacation packages and airline tickets. 
