Cishet, Cishetallo, Pericishet, or Monocishet is a term used by LGBTQ+ people to easily describe people who are not members of the community in any way, shape or form. This means people who are simultaneously cisgender, heterosexual, heteroromantic, allosexual, alloromantic, monogamous, and dyadic. The term originated within the trans community, particularly among straight trans people, and was created as a way to specify something who is not part of the LGBT+ community by virtue of orientation or gender.
Exclusionists have often used the term cishet to try to erase a-spec people (particularly heteroromantic asexuals and aromantic heterosexuals) from the community as they use the term to imply that a-specs aren't inherently LGBT+ by being a-spec. These people will sometimes use "cishet" as a code word for asexual heteroromantics and/or aromantic heterosexual (and sometimes a-spec people in general).
The term "cishetallo" or "cisallohet" or "allocishet" is sometimes preferable to make it clear that one is not referring to a-specs.
Some use the term "pericishet" (perisex cishet) or "dycishet" (dyadic cishet) to refer to cishet people who are also perisex/dyadic (not intersex), to show that intersex people have a place in the LGBT+ community by virtue of being intersex, even without orientation or gender.