Collaboration is a process in which autonomous actors interact through formal and informal negotiation, jointly creating rules and structures governing their relationships and ways to act or decide on the issues that brought them together; it is a process involving shared norms and mutually beneficial interactions.
Gray(1989)Collaborating: Finding Common Ground for Multiparty Problems
Collaboration represents a longer-term integrated process through which parties who see different aspects of a problem...constructively explore their differences...search for solutions that go beyond their own limited wision of what is possible
Bryson et al(2006)
We thus define cross-sector collaboration as the linking or sharing of information, resources, activities, and capabilities by organizations in two or more sectors to achieve jointly an outcome that could not be achieved by organizations in one sector separately.