Aceflexible or Flexible Asexual is a category for a type of asexual who is mostly asexual and occasionally experiences sexual attraction, but for this to be so little and so rare that one would still consider themself asexual with the sexual fluidity and would fit the "little to no" attraction definition included in asexual, something that distinguishes an aceflexible from a greysexuaI and could be considered the second definition of asexual given a new name. This could also be seen as similar to caligosexual, with the main difference being that it happens rarely. Another definition is about an asexual who is open to the idea of sex, often as a result of wanting to please their romantic partner. Some flexible asexuals may enjoy sexual intercourse on the odd occasion in which they partake in it. This also includes asexuals who have experienced experimenting with sexual activities, but not feeling any attraction or desire and for reasons unrelated to attraction (cupiosexuality, libido etc). Another example would be an asexual who associates libido or arousal with sensual attraction, but does not experience sexual attraction or an asexual who felt what can be described as sexual attraction, but not feeling like they fit the sexual category because it was only visual attraction (miransexual, desinosexual) thus does not change their orientation, but is notable enough to be included in ones identity. One may also prefer calling themself an aceflexible instead of a greysexual if they are enigmasexual and can't tell what genders they are attracted to because of how little their attraction is or because they found an exception of a person that they are able to find attractive, but are attracted to them more for who they are as a person and are not attracted to anyone else of that gender. Aceflexible may also be used because they don't want to place gender and attraction or simply feel that they don't have an actual orientation besides asexual. Similar to greysexual, it is very broad and can be both an umbrella term or an identity. It is similar to heteroflexible, homoflexible, biflexible, alloflexible, and greyflexible in concept of one primarily experiencing one orientation, but having some occasional alterations due to fluidity or other experiences, making it ampluspec.
An alternative definition, is one where the term "aceflexible" has the same meaning as dark greysexual .
History
Aceflexible was first coined in AVEN on February 9th 2013 in a AVEN thread discussing it made by the coiner. It was coined by AVEN user R_1. Aceflexible currently faces issues similar to semisexual to where it's not fully defined and hadn't reached a full understanding.
Aceflexibility as a concept was also mentioned by users on AVEN who didn't like the new redefinition of Asexuality as "little to no sexual attraction" instead of "no sexual attraction" and that Aceflexibility would make more sense to describe people whose attraction is so little and so rare as to seem nonexistent.
Resources
https://www.asexuality.org/en/topic/83926-ace-flexible-label/