The Wind in the Willows. You want to read the novel before you write the essay. If someone hides all the copies of the novel at the library and at the bookstores, you can't read the novel in time for your essay. That would be a breach of availability of that novel. One of the most serious and widespread problems in today's computers is called denial of service.
Denial of service can occur when someone overloads a computer system or network with bogus requests.
One writer received 20,000 e-mail messages in a single day. Imagine trying to find your own e-mail messages if someone sent you twenty thousand messages you did not want. It would take hours just to read through the subject lines to find the e-mail you wanted. That would be a denial of service. Denial of service is a breach of availability.