What is a CSV?
From ListBaby Wiki
CSV stands for "Comma Separated Values" and is a typical file extension for exported contact lists.
These documents basically separate out profile information by commas per row (name, Email, city, etc).
You can read more about what they are in general HERE
You can read about how to import .csv's into Listbaby HERE
You can read about how export your existing ListBaby contact list into a .csv HERE