Open: Learning is free from institutions or understood to be actively participating in non-institutional learning.
Critical: learning does no harm or actively works for social, economic, and environmental sustainability and resilience.
Participatory: learning is integrative and inclusive of participants regardless of skill level or pre-determined social hierarchy.
Networked: learning happens in a blended mesh. Learners, pedagogues, and others are nodes that exchange information to different degrees, depths and forms both online and in the field.
The best defense of these definitions I have found is presented here by Steven Downes:
Image above: Watts and Strogatz model/small world network graph, credit: Arpad Horvath