The collegiate National-minus difficulty (or Nats-minus) is intended to be similar to, but ultimately lesser in difficulty than, ACF Nationals and ICT. Tournaments at this difficulty have historically occupied the Spring Open slot immediately preceding the nationals season, acting as pre-Nationals.
The term was first used to describe a discrete difficulty level in the announcement of 2016 stanford housewrite, which established that the difficulty was on par with the earlier George Oppen and Cane Ridge Revival - those tournaments were in turn grounded by Minnesota Open. As with previous tournaments of the same difficulty, Nats-minus tournaments are generally created by one or more nationally competitive teams rather than by open writers and serve as a means of preparation for both the players writing them and the teams playing. This practice is likely a contributing factor for the tendency of Nats-minus, and indeed all comparable tournaments, to overshoot Nationals difficulty.