v1 stands for version 1: ArchiCAD for Mac (Mac OS X) releases are traditionally labeled as version, while ArchiCAD for Windows releases are labeled as Releases:
ArchiCAD 9 R1/v1 (build 1812) means the first version of ArchiCAD 9.
A version is different from a Hotfix in that it is usually distributed on CDs and has different localized language versions. Hotfix is download that is applicable to all language versions.