The separation to keep aircraft operating safely on final approach.
Examples are minimum radar separation to keep risk of collision to an acceptable safe level and wake turbulence radar separation to keep the risk of an adverse wake turbulence encounter to an acceptable safe level.
SESAR doc. 06.08.01 Operational Concept Description (OCD) and Operational Service and Environment Definition (OSED) for Time Based Separation for Arrivals (TBS), Ed 00.01.02 , 2013
Lexicon Release 2015.2