The definition of koinonia is fellowship, participation, contribution and sharing.
We generally think of koinonia in the context of the fellowship enjoyed by the early church in Acts 2:
Acts 2.42-47Because of this text we tend to think of koinonia in relational terms. Koinonia, we think, is about emotional intimacy. But koinonia is also used to describe sharing in concrete, material and monetary terms.
They devoted themselves to the apostles’ teaching and to koinonia, to the breaking of bread and to prayer. Everyone was filled with awe at the many wonders and signs performed by the apostles. All the believers were together and had everything in common. They sold property and possessions to give to anyone who had need. Every day they continued to meet together in the temple courts. They broke bread in their homes and ate together with glad and sincere hearts, praising God and enjoying the favor of all the people. And the Lord added to their number daily those who were being saved.
Actual money, when it's shared, is koinonia:
Romans 15.26We see this in Acts 2. Being devoted to koinonia involves material acts of sharing. Koinonia shouldn't be reduced to emotional closeness and social intimacy.
For Macedonia and Achaia were pleased to make a koinonia for the poor among the Lord’s people in Jerusalem.
Koinonia is sharing and fellowship that is concrete, material and sacrificial.