If the breasts or butt are naked, then it's still a problem. Generally, if it's not obviously sexual (for example, a drawing of an obvious sex act) then partial nudity that covers the breasts, butt, and genitals is OK.
Oh, and I should say that the most explicit upskirt or pantyshots (those where the genital region is very obvious) are also likely to be deleted.
Take a look at our webinar series -- where you can sign up to interact with Wikia staff, as well as watch past sessions
Be sure to check out Wiki Features to see what features you can enable on your wiki!
Explore our forums on Founder and Admin Central to see what other wiki admins are asking.
Lastly, visit our Help Pages to answer any specific question you may have.
All of the above links are a great place to start exploring Wikia. If you get stuck or have a question you can't find the answer to -- please contact us here. But most importantly, have fun! :)