A type of electrode used in electrostimulation, usually a dildo or plug shape, that fits in the vagina. Bipolar or single-ended are common variations. To form a circuit path, monopolar(single-ended) electrodes require another purpose-built electrode on the body or (non-purpose-built) metal object in contact with body, i.e. metal chair or leg cuffs. Note that pads and labial clamps are often used for external electrodes. They fit on opposite sides of the labia, usually.

Note that rather an electrode is anal or vaginal, depends on usage. It might make more sense to have electrode_in_pussy, electrode_in_anus, electrode_on_penis, electrode_on_balls, electrode_on_clitoris, electrode_on_pussy (external), electrode_in_urethra but this is a work in progress. If going that route, then the tags xxx_electrode should only apply to specific types of electrodes? For example, the dildo-style electrodes used in vaginal and anal penetration are generally bipolar or monopolar, but this is not very easy to see in most art, although it should be obvious in many cases due to laws of electricity. Pad(the tape style) electrodes and clamps are external use, generally. Cuffs go around appendages like a leg or penis.
Example of vaginal: post #2785025

Example of anal: (To be done/found, place in other article?)
Example of dildo electrodes: post #2098095
Example of pad electrodes: post #2908294
Example of (full circle) labial clamp (not being used as electrode, though) : post #2327306