A type of payout.
“Half face value of the ticket” means a payment in a situation when there is no univocal winner (2 winners), at the same time a bookmaker did not offer bets on the draw (in normal conditions usually it is only a single winner). If a winner is a single one, a payment achieves full size, so it is the “face value of a winning ticket”. But if there are several winners, face value is deducted to the number of winners (usually two winners) and the payment is 1/2 from the whole sum of win.
How to calculate the “half face value of the ticket”? A stake is divided by 2, multiplied by odds and then subtracted by the same stake divided by 2: [(Stake / 2) x (Odds - 1)] - (Stake / 2) = your possible winnings.