Generally speaking, someone whose primary sexual orientation is towards robots. They may be human or synthetic persons, and straight, gay, bi, etc is not specified. (Unfortunately, this word is often confused "romosexual," which is the only word that refers to someone who is both gay and a robot.)
Someone who loves getting sexual pleasures from mechanicaldevice s mimicking humans 'movements. In other words one who is sexually attracted to robots.
Scott: Hey look! I made this sex toy from our electric screwdriver!
Sean: OMG! You have to come clean to your parents. You are not a homosexual, you are a Robosexual!