Asexual (often shortened to ace) is a sexuality defined by a lack of sexual attraction. Being asexual does not mean that one is unable to experience romantic attraction, though some asexuals are also aromantic. Asexuals can have any romantic orientation.
It is important to note the difference between asexuality and celebiacy and abstainence. Those who are abstainent or celeibate choose so do to for moral or religious reasons. Whereas an asexual people may not participate in sexual activities do to a lack of attraction.
Although they lack sexual attraction some asexuals may still partake in sexual activities or be in sexual relationships. This could be for many reasons, such as, their own pleasure, the pleasure of a partner, or to have children.
Asexual can also be used as an umbrella term to describe someone on the asexual spectrum.
Etymology
The term asexual uses the Latin prefix a- which means 'a lack of'.