Software Defined anything (SDx) is a movement toward promoting a greater role for software systems in controlling different kinds of hardware - more specifically, making software more "in command" of multi-piece hardware systems and allowing for software control of a greater range of devices.
Software Defined Everything (SDx) includes
Software Defined Networks (SDN)
Software Defined Computing (SDC)
Software Defined Storage (SDS)
Software Defined Data Centers (SDDC)