ERF
From NWNWiki
ERF is an acronym for Encapsulated Resource File, a BioWare file type containing multiple game resources. This is a "container file format", similar to .rar, .tar, or .zip, without compression. Neverwinter Nights files that use the ERF format include imports/exports to/from the Toolset (.erf), hak paks (.hak), modules (.mod), and BioWare modules (.nwm).
The .erf extension is used to indicate a file containing resources exported from a module. This file type is the primary method of transferring objects from one module to another.
