From WordNet (r) 2.0 (August 2003) [wn]:
electronics
n : the branch of physics that deals with the emission and
effects of electrons and with the use of electronic
devices
From The Collaborative International Dictionary of English v.0.48 [gcide]:
electronics \electronics\ n.
1. the branch of physics that deals with the behavior of
electrons. Electronics is primarily concerned with
phenomena other than simple conduction, such as emission
of electrons, storage of electrical charge, the effects of
electrical fields on the conduction of electrons through a
circuit, and amplification and manipulation of electric
signals such as voltage or current by design of circuits.
Electronics also encompasses the application of such
fundamental principles to the construction of devices
using the manipulation of electrons in their operation,
known as electronic devices.
[PJC]
2. the branch of engineering concerned with design of devices
using the principles of electronics, for practical
purposes.
[PJC]
3. electronic devices generally, or the electronic circuits
within an electronic device. The Russian harvesters are
sturdily constructed, but their electronics are primitive.
[PJC]