A Content Delivery Network or CDN is a globally distributed network of highly optimized servers deployed in multiple data centers. It serves end-users closest to those centers therefore delivering content with high availability and high performance.
jQuery Easy uses the Google CDN to deliver jQuery-related script libraries and stylesheets (except Migrate, which is delivered by the jQuery's own CDN, Migrate is not hosted by Google).
It is preferable to use a CDN over your website's server to deliver the libraries needed by the plugin (when you select a version number in the plugin, you actually select a version that will be loaded by a CDN). It will most likely will make your pages load faster.