The quality (explicitly positive) of a woman's legs when they closely resemble legs found on many attractive women of the eighties. (Leg warmers optional, but equally amiable)
To be more descriptive and less analogous, Eighties Legs provide a marked voluptuousness that is made present by a moderated amount of exercise and healthy eating. Contrast between the upper thigh and lower thigh is high, with the calves being nothing if not dainty.
"Damn, that girl has Eighties' Legs!"
"What are Eighties' Legs?"
"Haven't you seen Ghostbusters? You need to get out less."