Demisexual is a term used to describe those who do not experience sexual attraction to others unless they form a strong emotional bond with someone first.
Demisexual people may still experience romantic attraction, but until a deep connection is formed, there is no sexual attraction involved. They may have little to no interest in sex and may only experience sexual attraction rarely, but that is not the case with all demisexuals.
Demisexuality is included on the asexual spectrum, but demisexual people can be gay, straight, bisexual, or any other orientation in addition to being demisexual.