PL/I ("Programming Language One", pronounced "pee-el-one") is a procedural, imperative computer programming language designed for scientific, engineering, business and systems programming applications. It has been used by various academic, commercial and industrial organizations since it was introduced in the 1960s, and continues to be actively used as of 2011.
PL/I's principal domains are data processing, numerical computation, scientific computing, and systems programming; it supports recursion, structured programming, linked data structure handling, fixed-point, floating-point, complex, character string handling, and bit string handling. The language syntax is English-like and suited for describing complex data formats, with a wide set of functions available to verify and manipulate them.
Read more about PL/I: Early History, Goals and Principles, Language Summary, Standardization, Usage, Evolution of The PL/I Language