The purpose of this Recommendation is to provide definitions of terms relevant to optical fibre submarine cable systems. A small number of terms defined in this Recommendation are associated with definitions in [ITU-T G.601], [ITU-T G.602] and [ITU-T G.701]. References to these definitions are given in parenthesis as an aid to ensure consistency between the different Recommendations in the event of future amendments. Figure 1 of [ITU-T G.971] shows the basic concept of optical fibre submarine cable systems and boundaries. Optical submarine repeaters or optical submarine branching units could be included, depending on each system requirement. In Figure 1 of [ITU-T G.971], A denotes the system interfaces at the terminal station (where the system can be interfaced to terrestrial digital links or to other submarine cable systems) and B denotes beach joints or landing points. Letters in brackets in the definitions of this Recommendation refer to the above figure.