Definition:

CDN refers to the Content Delivery Network. It is a method of geographically disbursed servers devised to enhance the performance of web pages and files. CDN directs user inquiries to servers that are the most competent to assist them.

Information:

Assistance provided by CDN intends to enhance the agility and accessibility of web pages and files. A fast pace is significant to marketers due to its influence on metrics, like bounce rate, shopping cart abandonment, and profitability. Many kinds of research illustrate how an additional second (or a part of a second) can induce a percentage of web page visitants to exit the site.

There are several forms of CDN services, varying from costly enterprise solutions to affordable alternatives procured through WordPress plugins.

ROI calculations towards CDN services can prove to be complicated for more substantial organizations, though, on an elementary stage, it demands the expertise of expenses incurred for various serving techniques and the enhanced performance that can generate marginal profit.

Helpful Articles Related to CDN:

Why You Need a CDN for your WordPress Blog?
WPBeginner (October 8, 2014)

10 Free CDN Services to Speed Up WordPress
WPExplorer (July 9, 2013)

7 Reasons NOT to Use a Content Delivery Network
SitePoint (September 27, 2011)

7 Reasons to Use a Content Delivery Network
SitePoint (September 22, 2011)

Why should I use Google’s CDN for jQuery?
Stack Overflow (February 1, 2010)

Best way to use Google’s hosted jQuery, but fall back to my hosted library on Google fail
Stack Overflow (July 18, 2009)

Which CDN is the best bang for the buck?
Quora

CDN market share in the Datanyze Universe
Datanyze

CDN Usage Statistics
builtwith.com