Introduction Based on the Directive 2001/16/EC modified by Directive 2004/50/EC of the European Community and additional activities of a number of EC member states concerning \'Obstacle-free Travelling\' ERA published a Technical Specification Interoperability for \'People with Reduced Mobility (PRM)\' which was mandated by the EC. The objective of this TSI is to enhance the accessibility of rail transport to these persons. The definition of People with Reduced Mobility is in accordance with clause 2.2 of the TSI PRM. General - The definitions and requirements shall describe the utilisation of information by people with reduced mobility especially for people with hearing, visual or communication impairments. - This standard defines elements which are universally valid for obstacle free travelling such as lighting, contrast, tactile feedback, transmission of visual and acoustic information. The definitions and requirements of this standard shall be used for infrastructure as well as rolling stock applications. - The standard shall define aspects of accessibility (to Infrastructure and Rolling Stock) specifically required by PRM users, it shall not define general requirements and definitions applicable to all users. - For preparing the terms and definitions well-defined operating conditions are to be considered. Any damages or operating trouble e.g. failures of parts of the lighting system will not be taken into account. Definition of systems and components - Part 1 Contrast Terms and definitions for systems and components The task is to describe clear and consistent terms and definitions. Where measurement methods and/or assessment procedures are needed to allow a clear pass/fail assessment, this task shall be done as well. Existing European standards shall be taken into account for this work.