Monogender, also known as unigender, is the experience of having only one gender. This can be any gender as long as it is only a single gender. The gender isn't necessarily static or stable, a genderfluid and/or genderflux person could be monogender, assuming they only ever experience a single gender at a time. It's the opposite of multigender/plurigender.
The first Monogender flag was made by tumblr user thesagasaurus and posted by tumblr user beyond-mogai-pride-flags on January 16th, 2018. It has no known meanings.
The second Monogender flag was made by arco-pluris and posted by Deviantart user pride-flags on March 24th, 2021. It has no known meanings.
The third Monogender flag was made by Reddit user u/Agreeable-Finish-376 on September 19th, 2022. The color meanings are Dark Grey for "all genders as one", Dark blue for masculine genders, Light pink for feminine genders, and Light green for Non-binary genders.