A device or system not directly connected to the CPU is?
A device or system not directly connected to the CPU is Off-line.
A computer may have more than 1 CPUs! Several servers are equipped with 2 or 4 CPUs. So just like the normal definition of "online"/"offline", a CPU that is powered ON is ONline, and a CPU that is powered OFF, is OFFline... Hot-plugging is the ability to swap a particular component without turning the machine off.