A Template is a way of combining the dataflow basic building blocks into larger building blocks.
Once a DataFlow has been created, parts of it can be formed into a Template for future release (import/export)
See Doc
Creating a Template with nothing selected while on the Root Process Group will create a single Template that contains the entire flow.
The following is not included in the template:
Templates received from others can be imported or dragged onto the canvas.
Instantiate (ie added to the canvas)
A template can be exported as an XML file.