The theory behind shared internet access is that users of a service share facilities in order to save money. This is the typical community broadband model, whereby a number of customers access an internet connection and the cost of that connection is shared between them.
This is internet which is distributed between yourself and your neighbours. Various techniques are used in sharing this service. As such a number of terms are associated with this internet service which include contention ratio ranging from 1:2 to undisclosed ratio, traffic shaping, Fair Usage Policy, best effort, Upto, no guaranteed speed. Service is usually delivered and managed on a best effort basis, meaning that your ISP will try their hardest to provide a smooth service, but wont offer guarantees on performance, nor on response time in the event of an outage.