A hackintosh, while originally a term used to describe an Apple Lisa which has been modified to emulate a Macintosh, has more recently come to mean a standard X86 based desktop computer that has been designed and built with off the shelf parts in order to run Apple's OSX Operating System. This has been made possible due to Apple's chipset architecture switch in 2006 from the aging IBM PowerPC Architecture used in the G3, G4 and G5, to the x86 architecture in the Intel core 2 duo and Core 2 Quad CPUs. This architecture switch was originally seen as being controversial, but has led to great performance improvements in Apple based PCs.
Hackintoshes can be built for significantly less money than purchasing a similarly specced Apple Computer, and therefore is are an attractive option for those who are still looking to run the OSX operating system. At present, building a hackintosh is against the EULA of Apple's OSX Operating System and is therefore of dubious legality. One company, Psystar, had built a business around producing and selling hackintosh based PCs, but was sued by Apple and forced to discontinue it's operations.