Windows 8 has 4 primary editions: Windows 8 (Core), Windows 8 Pro, Windows 8 Enterprise and Windows 8 RT. Windows 8 (Core) is often marketed as simply Windows 8 but many technical docs and other sources refer to it as Core to avoid confusion.
Wikipedia
Windows 8, a major release of the Microsoft Windows operating system, was available in four different editions: Windows 8 (Core), Pro, Enterprise, and RT. Only Windows 8 (Core) and Pro were widely available at retailers. The other editions focus on other markets, such as embedded systems or enterprise. All editions support 32-bit IA-32 CPUs and x64 CPUs.