An Android is a robot that looks very similar to humans. In TV shows and movies, androids are usually represented by human actors without special effects, while robots are usually shown in clunky suits or in makeup. Interestingly, androids in media tend to be meaner and colder than obvious robots. This is because the audience needs something to identify the android by, so they know it's an android.
In real life, androids do exist-- but they are inhuman and tend to look scary, falling into the uncanny valley.