Inside information is where people who have close connections with a horse know how likely it is that the horse is going to run in a certain race, and if it does, how well it is likely to run.
It is information that is known by those who work closely with the horse such as an Owner, Trainer, Rider, Stable Employee or their Service Providers. Service providers are people like vets, farriers and feedmen that have provided services to do with the horse. The information that a service provider may be privy to will only be valid for a period of 21 days or until such times as the information is put into the public domain.
It’s also information that is not in the public domain – so it has not been published, is not on public record and is not easily accessible by an interested member of the public.