The CNAME (A Canonical Name record) is a way of pointing sub-domains at a different servers to the main host. Thus http://blog.gdknowledge.co.uk may be pointed to a different server such as http://gdknowledge.co.uk.
It is an industry standard way of dividing up different functionality on a website. Many organisations, for example, use client.acmeco.com to host client-specific content behind a login, with the content hosted by a third party that specialises in building client portal (extranet) applications.
Passle has a similar solution. By using the Domain Name Servers, each Passle page can have a unique sub-domain name, for example: insights.gdknowledge.co.uk.
The entire page can be 'skinned' in your existing website design (so there is very little difference in navigation or look & feel).
Watch the video on why it's useful.