In general, a bridge is a direct tie between nodes that would otherwise be in disconnected components of the graph.
[1] This means that say that A and B make up a social networking graph,
would then represent the relationship between that corporation and Congress that only exists through the lobbyist.
This is very similar to the concept of a bridge in graph theory, but with special social networking properties such as strong and weak ties.
Also if the local bridge is deleted the distance between these two nodes will be increased to a value strictly more than two.
[3] In social networks, bridge relationships transmit information from one group to another.
Author Malcolm Gladwell characterizes people that habitually act as bridges as Connectors in his book The Tipping Point.
Bridges and local bridges are powerful ways to convey awareness of new things, but they are weak at transmitting behaviors that are in some way risky or costly to adopt.
Weak ties are able to spread awareness of a joke or an on-line video with remarkable speed, but political mobilization moves more sluggishly, needing to gain momentum within neighborhoods and small communities.
McAdams observed that strong ties, rather than weak ties, played a much more dominant role in recruitment to Freedom Summer on college campuses in the 1960s.