Facebook has updated its "community standards" for its 1.4 billion users, getting super-specific about what is and isn't allowed on the social network.

For instance, Facebook (FB) clarified what constitutes nudity (genitals, fully exposed buttocks and female breasts if they include the nipple -- except if the women are breastfeeding or showing post-mastectomy scars).

Nude illustrations are fine, as long as they're for educational or satirical purposes and aren't "explicit."

And so-called revenge porn, in which someone posts sexual images of another person without permission, is not allowed.

Hate speech has been another tricky topic for Facebook. The company said attacks on race, ethnicity, national origin, religion, sexual orientation, gender and "serious" disabilities are banned.

These distinctions have become necessary, because Facebook walks a thin line as it tries to police speech that spans dozens of countries and more than a billion people.

Facebook has run afoul of various interest groups and users when it has taken down controversial posts, including beheadings (which it then re-allowed and then re-banned last year). The company has inconsistently banned some hate speech, protests and nudity.

"It's a challenge to maintain one set of standards that meets the needs of a diverse global community," said Monika Bickert, Facebook's head of global policy management, and Chris Sonderby, Facebook's deputy general counsel, in a blog post. "For one thing, people from different backgrounds may have different ideas about what's appropriate to share -- a video posted as a joke by one person might be upsetting to someone else, but it may not violate our standards."

By clarifying its rules, Facebook said it hopes to explain more precisely why some posts and profiles stay up while others are taken down. The standards aren't new, Facebook says -- it only sought to clear up any misunderstandings.

"We have a set of Community Standards that are designed to help people understand what is acceptable to share on Facebook," Facebook said. "These standards are designed to create an environment where people feel motivated and empowered to treat each other with empathy and respect."

In addition to nudity and hate speech, Facebook gave extra emphasis to what constitutes self-injury, dangerous organizations, bullying and harassment, criminal activity, sexual violence and exploitation, violence and graphic content.

But the updated guidelines also clarify some other hot-buttion issues, including something seemingly as benign as what name you use. Recently, Facebook became embroiled in a debate with San Francisco drag queens who wanted to use their stage names rather than their legal names. Facebook ultimately gave in, and this week the company clarified that people must use their "authentic identities," which are the names that they are generally known by.

Facebook acknowledged that its policies "won't perfectly address every piece of content," but it will continue to address cases on an individual basis, when possible. It will also keep relying on the community to flag what it deems to be inappropriate content. Users can report troubling posts to Facebook by clicking the "Report" link at the top, right-hand corner of the page or app.