shell
shell: [orig. Multics n. techspeak, widely propagated via
Unix] 1. [techspeak] The command interpreter used to pass commands
to an operating system; so called because it is the part of the
operating system that interfaces with the outside world. 2. More
generally, any interface program that mediates access to a special
resource or server for convenience, efficiency, or security
reasons; for this meaning, the usage is usually `a shell around'
whatever. This sort of program is also called a `wrapper'. 3. A
skeleton program, created by hand or by another program (like, say,
a parser generator), which provides the necessary incantations to
set up some task and the control flow to drive it (the term driver
is sometimes used synonymously). The user is meant to fill in
whatever code is needed to get real work done. This usage is common
in the AI and Microsoft Windows worlds, and confuses Unix hackers.
Historical note: Apparently, the original Multics shell (sense 1)
was so called because it was a shell (sense 3); it ran user programs
not by starting up separate processes, but by dynamically linking
the programs into its own code, calling them as subroutines, and
then dynamically de-linking them on return. The VMS command
interpreter still does something very like this.
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