Naming an RPM ("redhat package manager") file with noarch indicates it's architecture independant - in other words, it doesn't contain any binaries specific to an Intel, PowerPC, StrongARM, Alpha, or other platform. Usually noarch RPMs contain shell scripts, config files, and other data that does not require a particular CPU type to work.
i386 on the other hand indicates the RPM contains binary executables that require an Intel 386 CPU or higher to execute.