When you disconnect something, you detach or separate it from something else. If you work plowing driveways during the winter, you need to disconnect the plow from your truck in the spring.
You can disconnect toy train cars, and you can also disconnect your laptop from its charger. In fact, unplugging electrical appliances is another way to disconnect something. Disconnect also means a lack of understanding or connection. So there might be a disconnect between you and your brother, or between what a politician promises to do and what she actually does. Disconnect combines dis-, "the opposite of" with connect, from the Latin conectere, "join together."