what does backbone mapping mean

[988ellsworth731krell881]

What does the term backbone mapping mean in this context?I need to add the following fields in a program\[code\]Field Name: ---- Backbone Mapping: ---- Type:Toll Free Number - SCAddress.AFTollFreeNumber String[20] Secondary Phone Number : SCAddress.AFSecondaryPhone String[20] \[/code\]I need to add this to the PersonPartiesLoaderSpec.xml file and the PersonPartyData.csv file