The "rough-in" is the term used for the phase of installation (of plumbing, electrical, etc.) when the entire system has been assembled and installed, but has not yet been connected to an outside power source or sewage system.
The purpose of the rough-in stage of installation is to help ensure that the installation has been performed properly and that the system will operate as safely as possible. Before the final connect, the rough-in system is inspected to make sure there were no mistakes made that could prove hazardous once the system is operational.
Plumbing is one of the household systems to which the rough-in rule applies. A rough-in faucet valve is a faucet that is part of a plumbing system that has been installed but is not yet connected to outside sewage.