A workflow file is a container for the individual workflow components associated with an object, including WorkflowAlert, WorkflowFieldUpdate, WorkflowOutboundMessage, WorkflowRule, and WorkflowTask.

Sample Package.xml:

<?xml version="1.0" encoding="UTF-8"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
    <types>
  <members>*</members>
  <name>Workflow</name>
 </types>
 <version>30.0</version>
</Package>