CDN is Content Delivery Network which is fundamentally an extensive conveyed arrangement of servers which sent in various server centers over the web. It helps in reducing load time of a page by offering documents at a higher data transfer capacity from a server that is physically nearer to your guest than your web server may be.
Goal of CDN:
Serve content to end-users with high availability.
Reason behind the use of CDN to host jQuery :-
It reduces the load from your server.
It saves bandwidth.
The most essential advantage is that it will be reserved if the client has gone to any site which is utilizing jQuery framework from any of the CDN.