The "odds" (probability) that a particular event will occur is usually expressed as a decimal fraction (0.50) or a percentage (50%) in academic studies.
But in gambling, what people are interested in is how much they stand to win or lose; so UK† bookmakers usually cite the odds as a pair of numbers X-Y, or X:Y, or X to Y.
In this notation the first number is the amount the bookmaker will pay you if you win, and the second is the amount you must stake. For instance, if the odds are "5 to 1" that a particular horse will win a race, you must pay the bookie one dollar (or Euro or pound or whatever). If the horse does not win, the bookie keeps your dollar; if the horse does win, the bookie returns your dollar and adds five dollars more.
Long and short odds refer to the size of the first number relative to the second. 20-1 or would be long odds; 1-20 would be short odds. (Short odds, however, are often quoted the other way around “20 to 1” with the tag “odds on”.)
In your example, the Wolf Hall's 10-11 quote means that the bookie requires you to pay 11 pounds for the opportunity to win 10 pounds. That's short odds for a contest with six contestants, where the result is entirely dependent on the subjective judgments of a panel of five judges.
Keep in mind, however, that bookmakers are not speculating on the probability that a particular work will win. They are more concerned with balancing out the amounts wagered, and offer odds calculated to insure that they take in more money than they pay out, whatever novel wins. Wolf Hall's short odds almost certainly reflect an unusually large number of bets on the book.
†American bookmakers use a different system, which provides a single number: a positive number is what is won on a $100 wager, a negative number is what must be wagered to win $100. For most sports two sets of odds are are quoted: a “moneyline” is a bet on one team to win outright, a”point spread” is a bet that the margin of victory will be greater or less than an announced handicap.