The part before the first colon specifies the access scheme or protocol. For HTTP, two slashes after the colon introduce a hostname. The next part is a pathname which is usually related to the pathname of a file on the server. The last (optional) part of the URL may be a query string preceded by ‘?’.
URI (Universal Resource Identifier)
URI is a formatted string that serves as an identifier for a resource on the Internet.
URIs that specify a common Internet protocol such as HTTP or FTP are also called URLs.
URI is a superset of URL.
For the sake of simplicity, you may treat URI and URL the same at this moment.
ICANN (Internet Corporation for Assigned Names and Numbers)
The non-profit corporation that was formed to assume responsibility for IP address allocation, protocol parameter assignment, domain name system management, and root server system management functions
