DEFINITION:
It includes:

• SSA (Space Situational Awareness): Space environmental effects that are limiting on all space missions and need to be assessed during all mission phases. Assessment requires the creation of environment models and the knowledge of effects, which is obtained by inflight measurement and testing.
• SST (Space Surveillance & Tracking): All aspects related to knowledge of the meteoroid and debris environment including space surveillance, databases, assessing debris risk levels for current and future missions, reentry of space objects , hyper-velocity impacts and protection , and mitigation measures.
• Clean Space related technologies: All the specific technologies (not included into other areas, although affecting to some of them) to develop an eco friendly approach to space activities.

(Source: ESA TD 4A, 4B and 4C for SSA, TD 11A and 11B for SST and PAE own elaboration based on Clean Space Program from ESA for 1 M 4)