Definition: PL/I

(Programming Language 1) A high-level IBM programming language introduced in 1964 with the System/360 series. PL/I was designed to combine features of COBOL and FORTRAN in order to eventually supplant them both, but that never happened. A PL/I program is made up of procedures (modules) that can be compiled independently. There is always a main procedure and zero or more additional ones. Functions, which pass arguments back and forth, are also provided.

PL/I programs are still running in legacy systems; however, like COBOL, there are not many programmers who know the language.