REXX program is also called exec

REXX programs have historically been called 'execs' because they originated on the CMS (Conversational Monitor System) and VM operating systems, where REXX files had a file type of EXEC. This terminology carried forward to MVS and TSO environments. A REXX exec is simply a REXX program stored in a PDS (Partitioned Data Set) member. The terms REXX program and exec are used interchangeably in mainframe documentation.