According to Wikipedia ... A Street team is a term used in marketing to describe a group of people who 'hit the streets' promoting an event or a product. 'Street Teams' are a powerful promotional tool that has been adopted industry wide as a standard line item in marketing budgets by entertainment companies, record labels, the tech industry, corporate brand marketers, new media companies and direct marketers worldwide. Street team members that are highly trained are now called Brand Ambassadors

But why not have a street team for the biggest of streets? The Information Super Highway

In a short amount of time you can get the members of your forum to do much of your work for you as far as promotion goes. All it takes is a little diddling on your end a couple of pep talks...

Trade their work for forum perks like bigger inboxes, larger avatars, a special forum just for them... granted most will only do a half-assed job, but still that's half a job you'll not need to be doing!

What work would they do? Blog commenting, forum posting, directory submissions (I took one of those huge free lists and cut it up into groups giving each member a section), some will even do article submissions for you!

One of the members on my street team handles the twittering for my site, another one added a live journal feed, another one handles my chat room... several things that have given me links, and lightened my work load....

For more detailed information check out my blog post:
Promote your forum with a Street Team