Computer networks are systems that connect multiple computers and devices to facilitate communication and data sharing. They enable the transmission of data over various transmission mediums, such as wired and wireless connections, and can range from small local area networks (LAN) within a single building to extensive wide area networks (WAN) that span multiple geographic locations. Key components of computer networks include network protocols, routers, switches, and network security measures, which together ensure efficient and secure operation. The development and management of these networks are essential for supporting modern digital communication, cloud computing, and internet services.