Mentalism, also known as sanism, is a form of discrimination and oppression against someone because of a mental trait or condition they have, or are judged to have. This may or may not be described in terms of mental disorder or disability. The discrimination could be based on stereotypes about individual differences or conditions (e.g. ADHD, bipolar, schizophrenia, personality disorder diagnoses), specific behavioral phenomena (e.g. stuttering, tics), or supposed intelligence, or neurology (e.g. neurodiversity on the autism spectrum).
Like other "isms" such as sexism and racism, mentalism is characterized by complex social inequalities in power. It can result in blatant mistreatment or multiple, small insults and indignities. It can influence how individuals are treated by the general public, by mental health professionals, and by institutions, including the legal system. The negative attitudes may also be internalized.
The terms mentalism (from mental) and sanism (from sane) are not currently in widespread use; concepts such as social stigma, and in some cases ableism, tend to be used in similar but not identical ways.
Read more about Mentalism (discrimination): Origin of Terms, Social Division, Clinical Terminology, Blame, Neglect, Institutional Discrimination, The Legal System, In Education, Multiple Discriminations