Aparigraha
Non-accumulation, non-coveting.

Outer level: Not acquiring too many possessions. Not obsessing over what we don't have. Not holding on too tightly to what we do have. Not wasting time in the upkeep, maintenance, and storage of possessions (including concepts) which don't serve to further one's contentment, knowledge, and growth.
Inner level:
Freedom from false identification with the things we have (or believe) as "who we are". Energetic freedom to give and receive freely. Being happy for the accomplishments and possessions of others and taking inspiration from that when appropriate, rather than becoming jealous.
Secret level: "When one is free from greed for possessions, knowledge of one's past and future lives unfold." Yoga Sutra II.39, Sadhana Pada, translation from BKS Iyengar's Light on Yoga Sutras

Further commentary is forthcoming....!

See also
Ahimsa, Asteya, Satya, Brahmacharya