Wikipedia
In computing, Interactive System Productivity Facility (ISPF) is a software product for the z/OS operating system that runs on IBM mainframes. It includes a screen editor, the user interface of which was emulated by some microcomputer editors sold commercially starting in the late 1980s, including SPFPC.
ISPF primarily provides an IBM 3270 terminal interface with a set of panels. Each panel may include menus and dialogs to run tools on the underlying Time Sharing Option (TSO). Generally, these panels just provide a convenient interface to do tasks—most of them execute modules of IBM mainframe utility programs to do the actual work. ISPF is frequently used to manipulate z/OS data sets via its Program Development Facility named ISPF/PDF, where PDF refers to Program Development Facility.
ISPF is user-extensible and it is often used as an application programming interface. Many vendors have created products for z/OS that use the ISPF interface.
An early version was called merely SPF and introduced in MVS system in 1974. Originally this stood for Structured Programming Facility, since it was introduced about the same time as structured programming concepts, but later the name was changed to System Productivity Facility. In 1985 IBM ported ISPF/PDF to its VM/SP operating system, where it was able to use either PDF or XEDIT as an editor.
ISPF can also be run from a z/OS batch job.