ICWS is yet another acronym and stands for International Core Wars Standard.

There are two types of standards out there:
ICWS'88 - an old school standard, with 9 simple instructions that support pre-decrement.
ICWS'94 - a much more complex instruction set, pre-increment and pre-decrement, post-increment and post-decrement, p-space and many other nifty things you can dwelve into if you visit www.koth.org .