Tacky is a dirt track with moisture still in it — a wet, sticky racing surface that holds the tire and lets cars dig in. Racers also call it heavy or black.
NASCAR’s dirt glossary defines it as “when the dirt racing surface is wet, which holds moisture and is sticky.” A tacky track is the high-grip end of the night: the tires throw dirt, you can stand on the throttle off the bottom, and the car will take a tighter, more planted setup because there’s bite to lean on. General direction is more cross-weight, more air, and more aggressive tire prep than you’d run when it goes away. Most nights start here and trend the other way — hot laps tacky, feature slick — so a setup that’s perfect at 6 p.m. can be junk at 10. Tag every setup sheet with the condition or the numbers don’t compare.
Tacky and slick want opposite setups, so misreading the surface means you're tuning for a racetrack that isn't there anymore.