A type of horse racing betting market offered days, weeks, or even months in advance, when the final field hasn't been finalized yet.
Usually, if your selected horse gets scratched, or for whatever reason doesn't start in the race, you aren't refunded your stake.
"I chucked ten bucks on this smoky in the Caulfield Cup, but he didn't qualify and I lost my money! Didn't realize it was an all in market."
