Internetsexual is a sexual attraction to people online, for example on social media. People who are internetsexual can have long distance relationships. In most cases, if you meet that person in real life you will no longer feel attraction towards them.
Other sexualities/genders
Internetsexual isn't connected to any gender or other sexuality, one can be heterosexual, lesbian, etc. It is an extra term to identify oneself with.