I just found the trencker tag on an old post. This seems to be from Japanese トレンカ, which itself is from Luis Trenker. Its name varies on English-translated Japanese product listings. Wikipedia's English article is Stirrup pants. "Stirrup leggings" gets more google results.
The tag's posts are currently split between leggings and pantyhose. As far as I can tell, the difference according to Danbooru is just whether the foot is covered and so this straddles the two.
The leggings wiki says just to use stirrup legwear instead. The stirrup legwear wiki implies they'd be considered pantyhose.
The tag hasn't been touched since 2014 and isn't mentioned anywhere. I was initially going to suggest aliasing it, but if the current recommendation is to tag these as neither leggings nor pantyhose, but instead just lumped in stirrup legwear (which by its admittance is usually thighhighs) then I think there needs to be a different recommendation on how to tag this clothing.
Despite the recommendation, they usually do get tagged pantyhose or leggings. stirrup_legwear pantyhose is the best search to find them, but also often false positives of stirrup thighhighs alongside (or over) pantyhose. stirrup_legwear leggings has fewer results but looks like it might have been cleaned up at one point (and also has a lot of things that shouldn't qualify for either tag).
Leggings or pantyhose? Own tag or no?
