Semi-Bisexual is the "orientation" where one is "bisexual but attracted to only one gender". It is generally considered satirical and made to mock and discredit the wider LGBT+ community. Semi-bisexual would be heterosexuality, homosexuality, or other forms of monosexuality depending on the gender one is attracted to, but is primarily assumed to be used by (cisgender) heterosexuals, as an excuse to be in the LGBT+ community .
The main controversy is that semi-bisexual is inherently biphobic. It takes bisexuality, an already historically ostracized sexuality within the community, and removes its multisexuality to allow (presumably cis) straight people into the community. This erases and exacerbates the exclusion that bisexuals and other m-spec people have faced and continue to face within the community, and dangerously misconstrues m-spec identities.
The term was also likely created to mock the LGBT+ community by "forcing" them to accept cishet people into the community.
History and Reclamation
While there is no clear date, it is believed to have been coined in around 2018. In more recent years, there have been attempts to reclaim the term, however, it is more recognized as its un-reclaimed definition. The most commonly seen re-definition being "a term for bisexuals with a bigger preference for one gender but attracted to other genders". The reclamation is also controversial as it implies that bisexuals with a preference are "less bi", and perpetuates the stereotype that bisexuals with a preference are faking their bisexuality.
M-spec people who have a large preference for a certain gender or genders may identify as omnisexual, or use other terms such as bisexual gay, bisexual lesbian, achillean, or sapphic. Other labels can be found in the LGBTA Wiki's attraction categories.
Those who are attracted to multiple genders, but have a large preference for a single gender or multiple similar genders and do not feel bisexual or other multi-spectrum identities are fitting labels may identify as heteroflexible, homoflexible, or other -flexible labels. Those who are only sometimes attracted to multiple genders may be monoflexible, dellosexual, or abrosexual.
Another reclamation is "A bisexual who is not biromantic," or "a biromantic who is not bisexual." This would fall under the split attraction model (SAM).
Additionally, those who have sexual interaction with a gender they are not sexually attracted may be cupiohex, cupiogex, or other cupiosexual labels, instead of "semi-bisexual". Those who are bisexual, but don't date or have sexual interaction with a specific gender due to trauma may use stresexual.