The concept is simple: panties that are visible beneath one's pantyhose.
Examples: post #380879, post #579682, post #792837.
A few candidates for a tag name (with my vote going to the first variant) would include:
panties_under_pantyhose
panties_underneath_pantyhose
panties_below_pantyhose
panties_behind_pantyhose
The panties and pantyhose tags would obviously need to be implicated.
Thanks.
Updated by jxh2154