A post placed at a specified distance before the finishing post on a racecourse, which a horse must have passed when the winner finishes in order to qualify for a subsequent heat.
A horse that had not passed the distance post by the time the winner had got home was 'distanced' and eliminated from the next heat.
Most races have distance posts along the route, so you'll know how you are progressing.
Blacklock had a three length lead at the distance post.
Definition of distance post in US English:
distance post
noun
North American
A post placed at a specified distance before the finishing post on a racecourse, which a horse must have passed when the winner finishes in order to qualify for a subsequent heat.