A rainout is a race program cancelled or cut short by weather before it counts as complete, sending the track to a rain check, a rain date, or a makeup show, and deciding whether points and purse get paid.
Every rulebook draws the line somewhere different, and the line decides your money. IMCA says a program “is not considered a rainout unless qualifying races have been completed,” and if the feature is rained out and never made up, all drivers get last place points. Slinger Super Speedway uses a halfway test — more or less than half the laps or events determines complete or rained out. Complete, and drivers are paid and given points. Rained out, and there is no payout; show-up points only if all practice sessions ran, and your pit pass is good for re-entry the next time that division races. Grandstand side, Ohsweken Speedway issues no rain checks once seven races are complete and refunds only unrescheduled specials. IMCA allows double features only for rainout make-ups.
A rainout can cost you a full night's purse and hand you last-place points you did nothing to earn, so knowing your track's completion threshold tells you whether it is worth unloading when the radar looks bad.