Related Questions:
How do I set the external id of a Menu Item?
What is the external ID used for on a menu item?
Answer:
External IDs on Menu Items are used when Importing to link a Menu Item being imported to a possible matching Menu Item in Event Temple. This is used as the unique identifier so that duplicates are not created when doing an import. This field is typically used when migrating data from a different platform.
To manually set the External Id in Event Temple: