URLs are so common now that they appear with little or no explanation on TV commercials and bubble gum wrappers.
But the home page URLs you hear in the media are only a small subset of the many options available with this versatile form.
Not all URLs refer to HTTP. In fact, the URL form was devised as a universal method for several different Internet protocols.
The protocol portion of the URL is referred to as the scheme. The scheme identifies a protocol and therefore tells the computer how to interpret the rest of the URL. The general format for a URL is described in RFC 1738 as