Network topology
The topology of a computer network defines how that network is "laid out." Topologies can be either physical (meaning how the actual hardware is interconnected) or logical (meaning how that network is implemented by protocols in software).
There are numerous different basic network topologies (and many variations). Here are several examples, with diagrams:
Bus topology
A "bus network" is hooked together like stops on a Public Bus route, one after the other. Bus networks usually require terminators at each end of the network, to prevent echo of the signal. Popular ethernet networks that are so ubiquitous today are logical bus topologies.
Ring topology
A "ring network" is literally in the shape of a ring; devices reach each other by passing data around in a ring. Physical ring networks often use two or more rings to add a level of redundancy if one of the rings should fail.
Older token ring networks are a popular example of a bus topology. Fiber Distributed Data Interface is a more modern example as well.
Star topology
A star network has nodes surrounding a central point, so that it resembles a star when drawn. The black box in the center is usually a switch or hub.
Popular ethernet networks that are so ubiquitous today are physically star topologies
Mesh topology
A meshed network is fully redundant, that is any one node going down will not affect connectivity to any of the other nodes. Contrast this with a ring topology, where if one of the nodes went down or the physical lines connecting two nodes were cut, the entire ring would be taken down. This is one reason ring networks are often done in pairs.
Again, topologies can be either physical or logical; meaning the software running over a physical Star network can use tokens passed around (Tokens are used on ring networks.)