A weak tie for me is an email-only or phone-only relationship with someone. The weak ties in your network are important (and underrated). Virginia Postrel, in this Forbes article on networks, reminds us that people usually find jobs not through their close friends but through their weak ties. Excerpt:
To social scientists, a network (self-help or otherwise) usually implies a system that includes both subgroups in which everyone knows everyone else and "bridging ties," where an individual is connected to others outside those smaller circles. In an influential 1973 article, "The Strength of Weak Ties," sociologist Mark Granovetter, now a professor at Stanford, demonstrated that while job hunters use social connections to find work, they don't use close friends. Rather, survey respondents said they found jobs through acquaintances--old college friends, former colleagues, people they saw only occasionally or just happened to run into at the right moment. New information, about jobs or anything else, rarely comes from your close friends because they tend to know the same things and people you do. One reason online forums are so valuable to participants like Franks is that they connect lots of people who wouldn't otherwise know one another.