If there are, say, 8 ribbons in a class of 38, and the first horses, say 10 or 12 of them all score 78 or higher? That becomes the cut off score. The rest of the class will have no chance at a ribbon unless they score a 78 or above.
The judge still gives a score fo each on the card but the announcer does not read it out loud. They just say "below the cut off", likewise a printed results sheet will note BC.
It saves alot of embarassment sometimes. Kind of sucks if you go early in the order and pull a rail or something then have to hear "scores a 48".... Or see the result of all your prep work memorialized in print as a sucky score.
When opportunity knocks it's wearing overalls and looks like work.