Opaque Stockings - Stockings made of yarn which give them a heavier appearance (usually 40 denier or greater).
RHT - Abbreviation of reinforced heel and toe.

What Are Stockings ?

Cuban heel Stockings - Stockings with a heel made with folded over and sewn reinforcement.
Demi-toe Stockings - Stockings which have a reinforced toe with half the coverage on top as on the bottom. This results in a reinforcement that covers only the tip of the toes as opposed to the whole toe. These can be with or without a reinforced heel.
Denier Stocking # - The lower the denier number the sheerer the garment. Stockings knitted with a higher denier tend to be less sheer but more durable.
Fishnet Stockings - Knitted stockings with a very wide open knit resembling a fish net.
Fencenet Stockings - Similar to fishnet, but with a much wider pattern. These are sometimes worn over another pair of stockings or pantyhose, such as matte or opaque, with a contrasting colour.
Fully Fashioned Stockings - Full-fashioned stockings are knitted flat, the material is then cut and the two sides are then united by a seam up the back. Full-fashioned stockings were the most popular style until the 1960s.
Hold-up Stockings or Stay-up Stockings - Stocking that are held up by sewn-in elasticated bands (quite often a wide lace top band).
Matte Stockings - Stockings which have a dull or non-lustre finish.
Mock seam - A false seam sewn into the back of a seamless stocking.
Nude heel Stockings - Stockings without reinforcement in the heel area.

Open-toedStockings- Stocking that stop at the base of the toe with a piece that goes between the first and second toes to hold them down. They can be worn with some open-toed shoes, especially to show off pedicured toes.
Sandalfoot - Stockings with a nude toe, meaning no heavier yarn in the toe than is in the leg.
Seamed Stockings - Stockings manufactured in the old Full-Fashioned manner with a seam running up the back of the leg. In the past they were manufactured by cutting the fabric and then sewing it together. Today stockings are generally fully knitted and a fake or mock seam is added up the back for a particular fashion look.
Seamless Stockings - Stockings knit in one operation on circular machines (one continuous operation) so that no seaming is required up the back.
Sheer Stockings - Stockings generally of a 15 to 20 denier.
Knee-Highs - Stockings that terminate at or just barely below the knee.
Thigh-Highs - Stockings that terminate somewhere in the mid-thigh.
Ultra Sheee Stockings - A fine denier fiber which gives the ultimate in sheerness. Usually 10 denier.
Welt - A fabric knitted separately and machine-sewn to the top of a stocking. Knit in a heavier denier yarn and folded double to give strength for supporter fastening.

Reference: encyclopedia.thefreedictionary.com