Merkins are wigs for the pubic area, with origins dating back at least to the 15th century, when pubic hair was sometimes shaved to combat pubic lice; merkins were also worn to cover dermatologic evidence of syphilis. Via.
Modern-day merkins can be viewed in a Google Image search (mostly safe for work, depending on where you work), with subsections for Hollywood, burlesque, etc (even a face-hugger variant).
And for completeness of "things you wouldn't know," here are instructions on how to attach (and remove) a merkin.
Addendum: A tip of the hat to reader Drabkikker, who tracked down the fact that this photo is a bit of art that is the creation of a modern photographer. Merkins, however, were real, so I'll leave the post up for the educational value of the links.