The percentage of full thread depth engagement between the bolt and nut.
75% is standard for cut taps. Increasing from 75% to 100% adds only ~5% strength but dramatically increases tapping torque and tap breakage.
65% is typical for form (roll) taps, which displace material rather than cutting it.
The minor diameter shown is the tap drill target diameter for the selected percentage. The tap drill table shows the nearest standard drill sizes.