CDN

CDN is short for Content Delivery Network which is a network of servers that deliver cached static content (e.g., images, JavaScript files, and CSS stylesheet files that seldom, if ever, change) from websites to users based on the geographic location of the user. In this way, static content is provided by the closest server resulting in faster downloads. Dynamic content that requires access to the database is not suitable for a CDN.

 

Source: http://www.wpbeginner.com/beginners-guide/why-you-need-a-cdn-for-your-wordpress-blog-infographic/