URL
URL is the acronym for either uniform resource locator or universal resource locator. URL is a specific character string that constitutes a reference to a web resource.
Any URL specifies its location on a computer network and a mechanism for retrieving it. URLs consist of two mandatory fields, (a) type of resource such as https for webpages, ftps for file transfers, mailto for emails, etc., and (b) hostname, as well as of optional (c) one or more submomains and (d) a file name, if any.
A URL is technically a type of uniform resource identifier (URI) specific to the Internet resources, but in many technical documents and verbal discussions URL is often used as a synonym for URI.
Syntax
According to the Business Insider, Sir Timothy John Berners-Lee once said about the double slash in URLs,
Really, if you think about it, it doesn't need the //. I could have designed it not to have the //.
Sir Tim created the World Wide Web, HTML, DNS, and URL.
