The Free On-line Dictionary of Computing (30 December 2018):

environment variable
environment

    A variable that is bound in
   the current environment.  When evaluating an expression in
   some environment, the evaluation of a variable consists of
   looking up its name in the environment and substituting its
   value.

   Most programming languages have some concept of an environment
   but in Unix shell scripts it has a specific meaning
   slightly different from other contexts.  In shell scripts,
   environment variables are one kind of shell variable.  They
   differ from local variables and command line arguments in
   that they are inheritted by a child process.  Examples are
   the PATH variable that tells the shell the file system
   paths to search to find command executables and the TZ
   variable which contains the local time zone.  The variable
   called "SHELL" specifies the type of shell being used.

   These variables are used by commands or shell scripts to
   discover things about the environment they are operating in.
   Environment variables can be changed or created by the user
   or a program.

   To see a list of environment variables type "setenv" at the
   csh or tcsh prompt or "set" at the sh, bash, jsh
   or ksh prompt.

   In other programming languages, e.g. functional programming
   languages, the environment is extended with new bindings when
   a function's parameters are bound to its actual
   arguments or when new variables are declared.  In a
   block-structured procedural language, the environment
   usually consists of a linked list of activation records.

   (1999-01-26)