collective term for platforms and OS

Is there any useful collective term you use in your IT networks for server software that does not fall into an end user application, i..e the top level application, i.e. your ERP apps, payroll apps, accountancy apps etc. I am thinking stuff such as OS, SQL, Oracle, IIS, Apache, AD, Citrix etc. We need a useful collective term for anything that sits between hardware and the end application.