Implications of Change in Terminology The term ‘mental illness’ has been introduced in the BNSS without providing any definition. However, the BNS clarifies that ‘mental illness’ shall have the same meaning as provided under s.2(a) MHCA.[4] The MHCA defines ‘mental illness’ as ‘a substantial disorder of thinking, mood, perception, orientation or memory that grossly impairs judgment, […]