nipple rings
It is a ring piercing placed in the nipples or a ring-shaped nipple piercing. Use this if the piercing forms a closed loop of rigid material between both points of insertion into the skin.
If it is not a complete loop, or the loop is completed by non-rigid material such as chain, it should likely be tagged as nipple bar (and possibly nipple jewelry) instead.
Sometimes depicted with something attached to it, such as nipple jewelry, a nipple chain, nipple weights, or used condom.
Do not use when the rings are around the nipple and not embedded in it as a piercing would be. Use nipple sleeves in this case.