On all modelling assignments you should be prepared for at least some degree of nudity. It is a reasonable assumption that a model should not be all too prude. Still, it must be your choice.
For nude modelling, you will probably be a freelance model. Requirements vary. See also: life modelling.
Nude modelling in art and art photography
Nudes, artistic nudes, fine art nudes or simply body or figure is usually an artistic interpretation of the human body. Often very innocent, it can also be extremely explicit and sexually aggressive if it helps the artist get his or her message across. Whatever it is you are asked to do, even if you find it shocking at first, is never to titillate, but to aid artistic expression.
The question whether it is art or pornography is difficult to answer, especially as there is no universally accepted definition of what constitutes art and what separates art from craft or even pornography.
Pornography is commonly defined as the representation of the human body with the aim of sexual arousal. Then again, a work of art could have sexual arousal as its central theme.
Consider this: Some of Egon Schiele's (Austrian painter; 1890 - 1918) work is extremely explicit, sexually stimulating and was considered pornographic at the time. The same can be said for some of Gustav Klimt's (Austrian painter; 1862 - 1918) work, particularly his drawings. And yet, both are today considered to be among the greatest, most important artists.
Other types of nude modelling
There are many more types of nude work with even more names, which have nothing in common with artistic interpretation: adult, hardcore, open leg, Continental, boy/girl, girl/girl, boy/boy, etc., often simply referred to (rightly or not) as pornography. I cannot tell you much about this type of work because it is not my field.
The more explicit the work you are considering, the more difficult it is for you to say no if you do not want to do something.
Be careful when considering photo shoots that involve (foreign) travel. The offer of a few weeks in sunny California (or wherever) may be tempting but you may find yourself grounded in the middle of nowhere with your passport and return flight ticket confiscated, which makes you very vulnerable.
The type of nude modelling which is found on page 3 and in boys' magazines is covered under glamour modelling.
Photographer participation
Generally speaking, the photographer should make photographs, not participate in them. The problematic issue of photographer participation is discussed here.
If you decide to do nude modelling, it means that you are not wearing any clothes. Sounds obvious?
You cannot model nude but, at the same time, not want to show this or that part of your body. Favourite body parts that aspiring nude models want excluded from their nudity are bottom, breasts and nipples. If you model nude, it's all of you.
The term "implied nude" is a favourite with aspiring models who fancy the idea but promptly get frightened by their own courage.
It is also nonsensical. As we are all nude under our clothes, we would all be doing implied nudity all the time. You are either nude or not. There is no such thing as implied nude.
The artist may decide to partly cover you, but as a nude model you have to offer your whole body.
Make up your mind what you are prepared to do, then discuss and agree with the photographer in advance and in detail what is expected of you - and stick to it.
