Modules are code-based add-ons that extend Wagn's functionality.  Any customization to Wagn that cannot be done in cards is done in modules.  They open up many possibilities:

1. site managers can quickly (and affordably) extend Wagn for customized needs without impacting other Wagns
2. developers can contribute Wagn code without having to learn all the intricacies of Wagn's core
3. the community can grow by sharing and cultivating Wagn modules

The API for Wagn modules is rapidly maturing and will be stable in time for the Wagn 2.0 release.

Modules were formerly called "packs".  We are currently updating our documentation to reflect this name change, but in the meantime the words "pack" and "module" should be considered synonymous.