Network is a system in which many devices or machines connect together to communicate in a meaningful way. The meaningful way is achieved in networks by implementing some predefined rules called Protocols. A network is an adaptation of a society where we as humans are always connected to our people. If we find somebody we should connect, we connect by either sending or responding to the connection requests.
Even in technology, networks are designed in a way that if a machine wants to connect to another one, it either sends or responds to the connection requests. Though all of this happens in the criteria of some predefined rules and protocols like TCP, UDP, HTTP, SMTP and many more.
Networks can be classified based on many parameters. Likewise On the basis of standardization, Standard vs. Non-Standard. Similarly on the basis of transmission media, Wired vs. Wireless network.Even on the basis of ownership, Private vs. Public networks.
By the way, the most common classification of networks is based on the area that is covered by the network. Based on that, the classification is as follows:
A network that is spread over an area of a room or a floor or a building or a campus, can be regarded as a LAN. Usually LANs are created by individuals to operate the network services to a local area. For example: a college can have a LAN of some PCs, a hospital can have a LAN of some PCs, a railway station can have a LAN of some phones or PCs connected to a Wi-Fi router etc.
While learning about LANs, its important to keep in mind that there is no any set number that is specified as to be the maximum count of computers that can be in a LAN. In fact its all about area. Though a LAN can be extended to a bigger span as well but the basic definition of it is just what we've learnt above.
A MAN is a city or state level network that works to operate network services in a city or in a state. For example: City-wise cable TV network is a best example for a MAN. The cellular networks spread over an entire state are also MANs. In many countries, MANs are used to bring the services of WANs to the LANs so that those services can reach to the individual people.
Despite of the examples that we put-in in the favour of MANs, its important to understand that literally there is nothing like a MAN in standards. A MAN is just a network that covers an area that is bigger than a LAN but is smaller than a WAN.
WANs are those networks that are spanned over the entire globe. Usually we say that WANs have no boundary which means they can be used across the world. Internet and WWW are the best examples of WANs.
WANs are usually created by a group of companies/organizations that is setup to provide propritery network services to the owners and rented network services to those companies/organizations that cannot afford a propritery WAN.