That it is for the x86 architecture, as oppsed to the Alpha, Solaris, SGI, PPC, or ia64 archectiures. This binary will work on any x86 machine (80386 or higher, to be exact. Linux wont work on less than that ;D )
Some intelligent package maintainers use specific build parameters to make a binary that works on a 386, but is optimized for a 486/586/686 archetecture. Red Hat will do that for as much as is relevant. It generally will build for a 386, but with 686 optimizations (will run best on a 686).
And when I say 686, I mean p3/p4/athlon (I dont think p2s fall in this category, if they do, sue me ;D )