In order to understand what exactly network topologies are; we first have to understand the meaning of the term "network". The term "network" means a series of nodes or points (computers) interconnected with each other by communication paths or some kind of an interface, where as in networking the term "topology" refers to the arrangement of these nodes in a network or in other words it describes the layout of the connected devices.
There are five basic types of network topologies:
A Mesh network is one in which each node is interconnected to one another creating a point to point connection. Mesh topology is based on the concept of routes, which means that information that is sent from a source on a network can take different paths to reach its destination.
Arrangement of nodes in a network that uses the star topology is in such a way that each node is attached to one central point (hub, router or a switch). Central Point (hub) accepts data from sending computer and delivers it to the appropriate destination. This type of topology is the most expensive one as it requires more cable length and if the central point fails then all the attached nodes are disabled.
A network that uses ring topology is one in which the computers are connected in a closed loop, a cable connects the first computer to the second, another cable connects the second computer to the third and so on. Each node has a unique address, all information travels through the ring in one specific direction (clockwise or anti clockwise).
In a network when all the computers are attached to a single cable then this type of network is said to be using the bus topology. Computers attached to a bus network coordinate to ensure that only one computer sends information at any time. Both ends of the network must have terminators, entire networks fails to work if there is a cable failure.
Tree topology is commonly known as the "Expanded star" topology. It's a combination of bus and star topologies. In this type of network group of stations or nodes connected to each other using star topology are connected to one main linear bus cable. This type of arrangement is difficult to configure and if the linear bus fails then the entire network goes down.
There is another type of network topology known as the Hybrid Topology. Hybrid topology is just a combination of different types of topologies such as star, ring, bus, mesh etc. All the networks using different types of topologies are connected to one central point (hub). Hybrid topology is reliable and flexible and an effective form of topology.