"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:

-Ampallangs
-Anal
-Apadravyas
-Deep PAs
-Dolphins
-Dydoes
-Foreskin Piercings
-Frenums
-Guiches
-Hafadas/Scrotals
-Nipples
-PAs (Prince Alberts)
-Pubics
-Prince's Wands
-Reverse PAs
-Scrotal Ladders

Some examples of adult piercings for females:

-Anal
-Christina
-Clitoris
-Fourchette
-Horizontal hood
-Hymen
-Inner labia
-Isabella
-Nipples
-Outer labia
-Princess albertina
-Triangle
-Vertical hood