The @jpd:xml-list annotation annotates business process variables of Untyped XML, specifically variables of type XmlObjectList.
An XMLObjectList data type represents a sequence of untyped XML format data. In other words, this data type represents a sequence of XML elements (a set of repeating elements) that is not valid against an XML Schema.
Business Process Variables and Data Types
For an example of working with XmlObjectList data types, see Step 9. Create Quote Document in the Tutorial: Building Your First Business Process.