Aceflexible (or Flexible Asexual) refers to those who are mostly asexual and occasionally experience sexual attraction; however, the attraction they experience is so little and/or rare that they consider themselves asexual with sexual fluidity. This would fit the "little to no attraction" definition of asexuality.
The term is sometimes given the same definition as dark greysexual. It is also used to define asexual individuals who are open to the idea of sex, often as a result of wanting to please their romantic partner. This includes those who have experimented with sexual activities, but who have not felt any attraction or desire. Another example would be someone who associates libido/arousal with sensual attraction but does not experience sexual attraction, or someone who experiences what can be described as sexual attraction, but who doesn't feel like they fit the sexual category because it was only visual attraction (eg. miransexual, desinosexual).
One may prefer calling themself aceflexible rather than greysexual if they are enigmasexual and can't tell what gender(s) they are attracted to, or because their attraction isn't based on gender. Aceflexible may also be used because one doesn't want to place gender and attraction, or simply feels 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. In concept, it is similar to heteroflexible, homoflexible, biflexible, alloflexible, and greyflexible, as one primarily experiences a single orientation with some occasional alterations due to fluidity or other experiences, making it amplusspec.
History
The term was coined by AVEN user R_1 on February 9, 2013.[1] Aceflexibility, as a concept, was also mentioned by users on AVEN who didn't like the redefining of asexuality as "little to no sexual attraction" rather than "no sexual attraction," and who thought that aceflexibility would make more sense to describe individuals whose attraction is so little and/or rare that it seems nonexistent.[2]