The question is common nowadays with people misquoting the term "gravure".According to some sources gravure is actually derived from the word photogravure or to be exact technically it's called rotogravure, a some kind of printing process used in the production of glossy magazines.How this got burst during the adaptation to Japanese language is unknown, but appealing abundant par for the advance of translated words in the Japanese language.In Japanese, it have been known that gravure is refering to glamour (not fashion) modelling, thus nude or non-nude photoshoot can be called as gravure style of photography.But, it is understandable that gravure idols will not doing sex act or porn although some of them doing some seduce acts that is similar of 'em but not with the guys but with the camera which is quite lol :p.
Okay, enough with the "gravure", now to the main question that we've been wondering a long time.So, we know that gravure is refering to modelling photoshooting in a "hot" way or "sexy" way, so technically we can say that gravure idols is "non-nude sex model" or "seduce model" or suitably a "bikini model" as i translate it directly by the meaning :p.However, they seem to be agreed that gravure idols is a bunch of sexy and beautiful japanese girls who is doing bikini photoshoot as well as semi-nude just for the sake of money pleasuring men indirectly if u know what i mean :p.They do it professionally though with the help of agencies that is providing the facilities to do it such as princess-collections which featured my all-time favourite gravure idol which Jun Natsukawa, one of the top model in this industry.
Nowadays, popular and attractive japanese gravure idols will not just focused on the increasing crowded niche industry only, of course for public exposure and money some of them trying their potential in the movies or tv shows industry like Aki Hoshino who is featuring in new Kamen Rider Movies and Live TV Show of Gokusen.Erika Toda. the actress of popular Death Note Live Action Movies also started as gravure idol before make it big in the filming industry in Japan.Although it is, some of them even tried the "darker area" or we can say porn industry which they called in Japan as JAV (Japanese Adult Video).Mihiro,Akiho Yoshizawa and the ever-growing-popular cute jav actress, Aino Kishi all started as gravure idols before sucking guys penis in a public :P.
People can watch this gravure idols in action by buying their DVD's and Photobook's where they usually sell for around US$30~40 for DVD's and US$10 for Photobook's.But, there's always an option if u having difficulties to buy 'em which u can go to http://japanesegravureidol.info/. A lot of DVDs and PhotoBooks in their site , reccomended for gravure idols lovers.