Short Circuit

Would someone kindly provide an idiot proof guide of:

1. What is a short circuit?
2. HOw does it occur?
3. How can it be prevented?
4. The reason I ask is I have been sent an email with the following snippet and was trying to understand what it meant. The email states:

'an accidental short of the wiring to a single pole RTE would actually short out the switch contacts and keep the release mechanism energised even when the RTE was operated!!'