Upon casual observation stockings may appear to be identical to thighhighs. For Danbooru purposes stockings are aliased to thighhighs due to their near identical nature.
By design, stockings require the use of a garter belt in order to stay up. Stockings are (generally) considered to be more upscale than thighhighs or pantyhose; the materials used are typically higher quality and of course, silk being the cream of the crop.
To search for stockings on Danbooru, lookup garter_belt; since stockings require the use of one when worn.
source: danbooru wiki