ProcessMaker refers to a connector as an integration with a third-party service that has configuration settings that make it easy for any Process Owner to indicate that the Process connects with a third-party service as part of a Request. Connectors are not part of the BPMN 2.0 specification; connectors extend ProcessMaker functionality outside of the BPMN 2.0 specification. A connector can be packaged and then installed to a ProcessMaker instance for any Process Owner in that organization to use. After the package is installed, the connector becomes available in Process Modeler.
After a connector's package is installed, its connector is available in Process Modeler. A connector functions similarly to a Process model element in Process Modeler: drag and place the connector into your Process model, and then configure it.
After the connector is configured and the BPMN-compliant Process is deployed, Requests for that Process use that configured connector. For example, if your Process model uses the Send Email connector, Requests for that Process can send email to specific email recipients during each Request's workflow using configuration settings you've specified.
Connectors, and packages to install them, can be created by the ProcessMaker open-source community. However, ProcessMaker provides connectors to Enterprise customers that are not available to the open-source community or the ProcessMaker open-source edition.