What is common to the alphabets x, q, z, and i, in the context of the Internet?
Answer: If you type x,q, i or z.com as the URL, it works. No, the other letters don't.
There are six single-letter domain names on the internet, which were registered before ICANN refused to distribute any more in 1993. They are, q.com for Qwest Communications; x.com owned by PayPal (it still works); z.com for Nissan's Z cars; i.net, a domain name registration company; q.net, for Q Networks; and x.org for the X.Org Foundation.
ICANN stopped giving out single-letter second-level domain names in 1993, because it was afraid that 'two-dot' domain names may not be enough to cover all the websites in the world, and it may need to use these single letter domain names to introduce another level (eg,: google.x.com ).
More nerd trivia.