Asexuality is one of many possible human sexual orientations, and is often abbreviated as "ace" or "A". At its most basic level, asexuality is simply a lack of desire for sexual intercourse with another person of either gender. Other than that basic definition, asexuality is very diverse. Some asexuals are also "a-romantic"--not into romance--and pursue friendships exclusively. Others want platonic romance with one gender or both, or simply have no gender preference. Asexuals may or may not have a physical sex drive, may or may not be squicked by sex, and may or may not enjoy kissing, hugging, going on dates, or other affectionate interaction. Asexuality is different from celibacy (though many asexuals are celibate) in that it is a naturally occurring orientation rather than a conscious decision to abstain from sex.
About 1% of the population of World One is asexual.
Canonically asexual characters are relatively rare in literature--few in number even compared to the relative rarity of homosexual and bisexual characters. Of course, most works which do not involve romance will not mention characters' sexual orientations, and fan writers are free to assign any orientation they desire, including asexuality, without breaking canon or writing an AU.
Non-human species in fiction may be asexual by nature because they do not use sexual reproduction. Robotic characters, shapeshifters, and non-physical entities are especially likely to be asexual. Some non-human species may be a-romantic, but not asexual, with reproduction unrelated to personal relationships.
Canonically asexual characters include:
- Sherlock Holmes
- Charlie Weasley, from Harry Potter, who is stated by Rowling to be neither gay nor interested in women
- Sheldon, from The Big Bang Theory
- Adrian Monk (asexual but not a-romantic)
- Peter Pan, who refuses to grow up; included here because JM Barrie, his author, was probably asexual.
- The Doctor from Doctor Who, in some of his incarnations.
Asexuality is often misrepresented in badfic:
- Asexuality may be shown as exclusively caused by trauma.
- Asexuality may be "cured" by healing sex.
- Asexuality may be assumed to be unnatural and a sign of psychological damage.
- Asexual characters may be represented as hating the opposite sex.
- Asexual characters may be assumed to be incapable of romance or friendship.