A Central Buffer Node is an object node for managing flows from multiple sources and destinations, represented in an Activity diagram. It acts as a buffer for multiple in-flows and out-flows from other object nodes, but does not connect directly to Actions.
OMG UML Specification
The OMG UML specification (UML Superstructure Specification, v2.1.1, pp. 350-351) states:
"A central buffer node gives additional support for queuing and competition between flowing objects .... A central buffer node accepts tokens from upstream object nodes and passes them along to downstream object nodes."