Severe Neurological Impairment: A delphi consensus-based definition

•Severe neurological impairment (SNI) is a term which has not been consistently defined.•Lack of an agreed definition can result in variance in reporting of research, including incidence and outcome measures.•The Delphi method has been successfully used as a method of reaching consensus, including the creation of definitions.•A consensus-based, international, multi-disciplinary definition of the term SNI has been formulated.•This definition can be used to perform consistent, reproducible research and for adequate service-planning.