This tag applies only to genitalia, sex acts, body fluids, or other things that would normally be censored. It does not apply to nipples, or to body parts that aren't fully visible.
In Japan, it is illegal to draw uncensored genitalia if they are to be published publicly for distribution. Some artists skirt around this law by applying censorship that is easy to remove, or by applying pointless censorship that barely hides the censored body part. Others maintain a non-Japanese presence to bypass Japanese laws altogether and distribute uncensored versions of their work. It is also noted that some censorship also doubles as a paywall or sample work of sorts, with the uncensored version available in an artists' donation page, such as Patreon.