In other words, a bridge is a link which ties together parts fo the network that otherwise would not be connected at all. A local bridge is a link between nodes A and B which, if removed, would mean that the shortest path linking A and B would be of at least length 3. The density of a network is defined as the number of ties present divided by the number of ties possible. It is the proportion of possible ties that actually exist. The speed with which information travels through a communication network from one node to another is a function of the number of links in the paths linking them.
Denser networks have shorter paths, so they transmit information more quickly.
Networks broken up into subgroups diffuse information quickly within groups, but have trouble getting information moving between groups. According to Granovetter, weak ties are particularly important in diffusion. Studies show that most jobs are obtained through network connections, and that among those getting a job via connections, the vast majority get them through weak ties. The reason is that strong ties create dense little knots of people who share and reshare the same old information. Novel information comes in from connections with people outside one's clique.