I'm not a computer scientists, but my understanding of a "handshake" in the computer world is when the end user (in this case, you) requests access to a site (by either clicking on a link in a page or entering a URL into the browser search bar), it goes through cyberspace until it reaches the destination site. Then it has to coordinate with the destination page to load the information into your browser window. Usually, it's a seamless process. But if there is a problem and the two parts don't coordinate properly for some reason, the handshake won't occur and there will be an error or a delay.