An IMS Enterprise data file could be intended for multiple "targets" - different LMSes, or different systems within a school/university. It's possible to specify in the Enterprise file that the data is intended for one or more named target systems, by naming them in <target> tags contained within the <properties> tag.

In general you don't need to worry about this. Leave the setting blank and Moodle will always process the data file, no matter whether a target is specified or not. Otherwise, fill in the exact name that will be output inside the <target> tag.