The short answer
Emerald is a gemstone: the bluish-green to green variety of beryl. Emerald cut describes a cutting style commonly associated with a rectangular outline, beveled corners and parallel rows of step facets. An emerald-cut diamond is diamond; an emerald-cut moissanite is moissanite. Neither becomes an emerald because of its outline.
What the step-cut look means
Broad, orderly facets create a geometric pattern and flashes of light different from many brilliant-cut styles. Emerald crystals helped make this outline popular for emerald gemstones, but cutters use it for other gem materials too. Shape and facet arrangement tell you about appearance, not chemical composition or origin.
Shopping for an emerald gemstone
Color is an important consideration, and inclusions are typical in emerald. Ask for gemstone identity, origin and treatment disclosures for the specific stone. The words green, emerald color and emerald cut alone do not establish that a stone is emerald. A laboratory-created emerald is also distinct from a green simulant.
Care follows the stone, not the cut name
Emeralds may have fracture-filling treatments. GIA recommends gentle warm soapy water and cautions against ultrasonic and steam cleaning. Follow the supplier’s instructions for the stone, treatments, metal and setting together. Do not apply a diamond-cleaning routine merely because the emerald has a similar outline.
A useful product checklist
Check the listed primary gemstone first, then cut or shape, dimensions, treatments, metal and available size. If a listing mixes center and accent stones without identifying the main gemstone, ask for clarification before purchase. Use Emerald Rings for the gemstone; use shape filters in All Jewelry when you want an emerald-cut outline across stones.