system used to be a synonym for 'end'. Now it is used, mainly in Headers files, to declare macros and extern consts in Carbon or other frameworks.

Syntax:
system ExistingTypeName nameOfConstVarOrMacro

Examples from Headers:
system CFDictionaryKeyCallBacks kCFTypeDictionaryKeyCallBacks
system CFBooleanRef kCFBooleanTrue
system CFBooleanRef kCFBooleanFalse

Example:

system double INFINITY
print INFINITY
stop