Connectors illustrate communication links between Parts to fulfill the structure's purpose, typically in a Composite Structure diagram. Each Connector end is distinct, controlling the communication pertaining to its connecting element. These elements can define constraints specifying this behavior. Connectors can have multiplicity.
OMG UML Specification:
The OMG Unified Modeling Language specification, (v2.5.1, p.227) states:
A Connector specifies links that enables communication between two or more instances. In contrast to Associations, which specify links between any instance of the associated Classifiers, Connectors specify links between instances playing the connected parts only.