fwiw there's a lot of semantic drift for these terms depending on country and language.
In Japan,
yaoi ("
yama nashi, ochi nashi, imi nashi") refers to doujinshi/works with m/m sex scenes, and has negative connotations. Nowadays
BL is the more commonly used term to very broadly refer to any works focused on m/m relationships that are targeted at women; including sex or not; professional or doujinshi; etc. Meanwhile, here in English people seem to draw the distinction where
yaoi which refers to explicit M/M, and
shounen ai which refers to non-explicit M/M.
All of which are distinct from
bara ("rose"), which denotes M/M works created by gay men for a gay male audience. (These are often more realistic/autobiographical.)
In Japan,
yuri ("lily") broadly denotes F/F works. Meanwhile, here in English, there seems to be a parallel distinction between
yuri and
shoujo ai wrt explicit/non-explicit; but that seems to have fallen out of use lately in the yuri community; In recent times, the meaning of yuri has basically drifted to more closely match Japanese usage. Dynasty Reader, a yuri-centric site, uses the yuri tag to denote all F/F works, and makes no use of a shoujo-ai tag.
Also, Seven Seas Entertainment has been licensing a lot of LGBT-related titles here in North America, and the
relevant genres they have only consist of
boys' love and
yuri; no
shounen ai,
shoujo ai, or
yaoi. Series like
Bloom Into You or
Nameless Asterism, which get classified as shoujo ai here, are actually marketed as yuri in the publishing world.
To me,
yuri means any work with a focus on a F/F relationship, explicit or non-explicit.
***
If we really wanted to be totally unambiguous, we could be like AO3 and just use
relationship tags of either F/F, F/M, M/M, or Gen tags +
an age rating of either general, teen, mature, or explicit ¯\_(ツ)_/¯ (on a related note, there was
a thread a while ago about having more rating level granularity for filters)
Or maybe we could just lay out more specific guidelines for genre tagging. I still think that the idea of a tag wiki is a sound one, even though it was shot down (
https://mangadex.org/thread/11565/wiki-guidelines-for-genres-and-tags)