A group of (one or more) computers connected together sharing resources accounts package, data, storage, backups, hardware, and software. Some of the most common networks are called local area network (LAN) and the wide area network (WAN).
LAN can range from a few computers (small office) to several thousand computers spread throughout multiple building (schools, large offices).
WAN expanding a LAN to encompass many geographic locations.
Computer Networks are the backbone of all modern businesses, everyone has a pc/mac for their accounts, email or Internet access. With different operating systems (Windows XP, Vista, Linux, Mac OS X) server software and applications.