The eBook Collection (EBSCOhost) (nlebk) database is:
A database that contains all of the full text eBooks that your institution purchases from EBSCO, including eBooks from your eBook Subscription Collections, as well as single eBook titles. When you acquire an EBSCO eBook it is automatically transferred into this database.
The eBook Index (edsebk) database in EBSCO Discovery Service is:
An index database that does not contain full text. This index of e-book citations offers the ability to link out to full text if you have access from any vendor. Full text is retrievable for those customers who purchase e-books from any of the publishers included. Full-text access is enabled through a CustomLink to bring you to the full text on the provider's site. The citations from Discovery e-books are available for all EDS subscribers.