A cameo habille (meaning 'dressed cameo' in French) is a 'jewel within a jewel,' a cameo in which the subject carved in the cameo (usually a woman) is wearing a miniature piece of jewelry (like a tiny diamond necklace with a stone embedded in the cameo)."Check out "Guilloche" and "Gutta percha" if you're interested in enamel and Victorian jewelry. This Illustrated Dictionary of Jewelry is so nice to have access to.
Another fabulous reference site for vintage jewelry collectors, sellers or buyers is Illusion Jewels' Researching Costume Jewelry marks page here. I've used the site innumerable times in my quest for the identification of vintage pieces I've bought and sold. Must sees are the Vintage Jewelry Patents and Vintage Jewelry Ads pages!
A more abbreviated but still informative page: Vintage Jewelry Research.
And if you're interested in American Indian jewelry, there are short but informative references at Hazelwoods' site.
And for those of you who love silver, this will come in very, very handy. The Online Encyclopedia of Silver Marks, Hallmarks & Makers' Marks is the last word on finding out what a little castle stamped on Grandma's sterling spoon means, or if your Mexican silver brooch was made before 1940 or 1980.