An outcast from society is someone who has been physically, mentally, emotionally or relationally expelled from involvement in a population. This expression most often refers to people considered abnormal or possessing undesirable qualities. Criminals, pedophiles, people with disabilities and the poor are examples of groups sometimes treated as outcasts.
A person is literally cast out when he is sent to prison or forced to leave a particular community. A homeless person is often considered an outcast, but homelessness is generally not the outcome of societal action specifically directed at an individual. Often, a person is treated as an outcast based on groupthink and peer pressure.