Foxtailing is also called Crowning. It can be genetic or it might be from too intense of light and/or high temps. It is basically a bunch of calyxes growing directly on top of one another and creates a long tail, crown or spire.
It doesn’t necessarily mean the nuggs will be less dense pre say, nor less potent, especially if it is mostly due to genetics.
The picture below is an example of extreme foxtails.
Happy growing,
MacG