“Adult piercing” is a term used for genital and nipple piercings. They usually serve sexual function, but some are done simply for aesthetic purposes. Trans-urethral piercings generally heal quickly and serve sexual function.
Functional adult piercings that are meant to take some abuse should be pierced at larger gauges. 12g is generally a minimum for these types of piercings, depending on anatomy.
Functional subdermal genital implants can vary from beads to domes to ribs. These are most commonly done to give the shaft of the penis a “ribbed” appearance and feel.
Some examples of adult piercings for males:
-PAs (Prince Alberts)
Some examples of adult piercings for females: