A Full Quad or Unicorn Quad is a polyamorous relationship between four people where all four people are dating each other. This can be considered a mix of a group relationship and a quad relationship.
History
It is unknown when the term was first coined however it is known to have been around since 2018.
Flag
The flag was coined by Tumblr user beyond-mogai-pride-flags on November 17th, 2018. It has no confirmed meaning.