Triad

A Triad, also called a Triangle or Delta, is a possible polyamorous relationship structure which involves three people who are all actively involved with the other two people. The type of relationship is sometimes called a throuple, a portmanteau of "three" and "couple".

History
It is unknown when the term was coined, however it has been around amongst the community for a number of years.

Flags
The first flag was coined by Deviantart user Non-Mono-Pride-Flags on January 15th of 2016. Red is for passion, grey is for stability, and purple is for sensuality.

The second flag was coined by Cryptocrew on January 31st of 2021. Purple represents stability, blue represents unity, pink represents consent, red represents passion and attraction (of any kind), grey represents non-conformity to societies expectations, black represents relationship, and white represents purity.

Resources

 * https://www.purewow.com/wellness/what-is-a-triad-relationship
 * https://affirmativecouch.com/polyamorous-relationship-structures/#:~:text=Triad%3A%20A%20triad%20is%20also,sexually%20involved%20with%20each%20other.
 * https://www.shape.com/lifestyle/sex-and-love/polyamorous-triad-what-its-like