A Content Distribution Network (CDN) is a network of servers distributed geographically. The purpose of a CDN is to deliver content on the internet much faster. If a user in Toronto is trying to access your website, the closest server to them will take care of this. But someone coming to your website from Sydney, Australia, will be catered to by a server closest to them. The main host server holds your website content, and all the other servers have a cached version each.

Until 1991, the Internet was restricted to use only "...for research and education in the sciences and engineering..."[1][2] and was used for email, telnet, FTP and USENET traffic—but only a tiny number of web pages. The World Wide Web protocols had only just been written[3][4] and not until the end of 1993 would there be a graphical web browser for Mac or Windows computers.[5] Even after there was some opening up of internet access, the situation was confused until 1995.[6]
While the ARPANET was being developed, computers connected to the network were typically mainframe computer systems that could be accessed from dumb terminals connected via serial ports. Since these terminals did not host software or perform computations themselves, they were not considered hosts as they were not connected to any IP network, and were not assigned IP addresses.
Note: The dual meanings "host"/"guest" of Latin hospes and its progeny are due to customs of reciprocity: a person serving as guest on one occasion would act—and be expected to act—as host on another occasion to a visiting former host. Both Latin hospes and Slavic gospodĭ have undergone a considerable degree of phonetic reduction from their putative etymons—in particular in the Slavic case, where Latin unstressed syllable reduction and syncope were not at play—leading some to question the correctness of the etymologies. Parallel compounds with the same second element are Greek despótēs "master, lord" (going back to *dems-pot- "master of the house"; see despot), Sanskrit dámpatiḥ "householder, lord of the house," Avestan də̄ṇg paitiš; Sanskrit viśpátiḥ "chief of a settlement/tribe," Avestan vīspaitiš, Lithuanian viẽšpats "lord" (with outcomes of Indo-European *u̯iḱ-, *u̯oiḱ- "house, community"; see vicinity). 

The host may also provide an interface or control panel for managing the Web server and installing scripts, as well as other modules and service applications like e-mail. A web server that does not use a control panel for managing the hosting account, is often referred to as a "headless" server. Some hosts specialize in certain software or services (e.g. e-commerce, blogs, etc.).