Ante-post betting, also known as futures betting, is when a fixed odds betting market exists in advance of an event. The definition of ante-post or futures betting is usually when there is betting on an event in the future (ie: when the event does not take place today but sometime after that).
An example of futures betting in sport may be betting on the winner of the World Cup or The Super Bowl, even though the final of that event may not take place for several weeks or months.
More specifically, in horseracing or dog racing, ante-post betting is when a fixed odds market exists prior to the final declaration stage of a race (usually 24 hours or more before a race).
Selections that are backed in horse or dog racing ante-post markets will be deemed to be losing bets if they become non-runners. It follows that there are never any Rule 4 deductions in the event of non-runners on ante-post betting, also known as futures betting.