Pluriad

Pluriad or Plurad is an umbrella term for any relationship involving more than two people where all of the members are actively involved with all other members of the relationship. It encompasses triad, quad (full quad), pentad, hexad, heptad, octad, ennead, nonad, decad, etc.

Pluriads are different to group relatonships in definition, as they're welcome to flings/one night stands, as they do not count as a true member to be involved with, since flings are usually a once or twice thing, rather than a consistent partner.

Flag
The Pluriad flag was coined by Tumblr user beyond-mogai-pride-flags on October 31st, 2018. It is said to be based off of the triad and quad flags.

Resources
https://beyond-mogai-pride-flags.tumblr.com/post/179628878130/pluriad-pride-flag