It’s a trigger that doesn’t trigger a sound, but will cause parameter locks to effect the current track .
If they’re pointing to vol/dist, these trigless trigs are either distorting the tail (if it’s pumped up) or silencing the tail (if it’s at a minimum) of the previous note being played. I suspect it’s to cut the volume to 0, enabling an instant mute effect on that step until another trigless trig affects volume, or a normal trig is played.
You can create one by pressing func then pressing a trigger. Hope this helps!