What is a scheme?

The scheme comes first in a URL.

If a URL is a postal address, the scheme is your mode of transport.

  Type Behaviour
http Web page Make a request to show the page
https Secure web page Make a request to show the page
ftp File transfer Login to the FTP server to download the file
mailto Email Open up your email client
file Local file Load the file from your local machine

Also known as a protocol.