BOP is a term for the muti gender attracted (m-spec) community. BOP is comprised of bi, omni, and pan/ply. Even if one doesn't identify with the labels mentioned, they can still be considered a part of the BOP community if they are attracted to two or more genders.
History
The term was coined by Tumblr user official-cisphobe on April 22, 2019.[1] The flags had previously been created by the same user on April 16, 2019.[2]