Susan is responsible for application development in her company. She wants to have all web applications tested before they are deployed live. She wants to use a test system that is identical to the live server. What is this called?

A test server should be identical to the production server. This can be used for functional testing as well as security testing, before deploying the application. The production server is the live server. A development server would be one the programmers use during development of a web application, and predeployment server is not a term typically used in the industry.