Horses that belong to one owner or under one trainer, running on the same race, are "coupled" together. This means that when you bet on one you also get the other for no additional charge. They will be listed with the same number with a the first available letter added to the second coupled horse.* Example: 1, 1A. If there are multiple pairs of coupled entries the next pair will be listed as 2, 2B, then 3, 3C, and so on. (More than 1 set of coupled entries is uncommon and more than 2 is very rare. Foreign tracks may list coupled entries differently.)
As a wager on one horse in a coupled entry counts as a wager on the other as well, you get paid out if either horse wins.
If both horses finish in the money then the higher payout will be applied. For combination payout purposes, with a Trifecta the fourth spot finisher will me marked as 3rd, and for Superfecta the 5th spot finisher will be marked as 4th.
If you placed a wager on a horse that is part of a coupled entry and your horse scratches you will have the other horse in its place. If both are scratched then the Scratched Runner Rules for that wager type will apply.
In French racing coupled runners are connected by letter, not number. For example, instead of a 1 and 1A, there could be a 7A and 9A. A second set of coupled runners would end with a B. They can be different places in the card like 8a/12a or 4b/9b.