From Computer History Wiki
Electronic means that a device depends on the controlled use of electrons. The controlling device is a vacuum tube or a transistor, but diodes, as well as other passive electrical devices (resistors, capacitors, and inductors) are usually also involved.
(Obviously all electrical devices, such as relays, light bulbs, etc, use electrons, but the term generally refers to those with controlling devices, as above.)
The plural form, electronics, is shorhand for hardware which is electronic in nature.