1 domain license provides an opportunity to have 1 domain name associated with one single database and one copy of the script (without redirects from one domain name to another).

Multi domain license lets you have an unlimited number of domain names associated with one database and one copy of the script (including redirects from one domain name to another). License cost does not depend on the number of domains.

Multi server license authorizes a set number of licenses installed under a set number of domain names. The software files may be located on different servers, directories, IP addresses. Basically, this option implies several independent sites, each one with its own domain name and database.