Here's USATF on the standard for records:
Record-Eligible - Indicates whether records may be set on the course. "wind-dependent" means a record can only be set when it can be shown that there is no significant tailwind. (Depends on drop and separation--see below)
Drop - Net elevation decrease from start to finish expressed as a fraction of the race distance in meters per kilometer (negative values indicate net climb). Courses with any amount of drop may be certified, but for record eligibility, drop must not exceed 1.0 m/km (USATF Rule 265.5).
Separation - Straight line distance between start and finish expressed as a percentage of the race distance. If separation does not exceed 30% and the course meets the drop limit, it is automatically eligible for records. If separation exceeds 30% but the course meets the drop limit, it is eligible for records when it can be shown that there is no significant tailwind.