A professional network is some sort of connected community of people, whether it’s an online community like LinkedIn or Women for Hire or simply your local Chamber of Commerce. I guess for some folks, even things like their local golf club (the group not the stick) can function as a professional network if it has business people they can connect with.
The purpose of a professional network is to help you grow your business, improve your career, network for jobs, meet like-minded people, and even help save your butt if you get in trouble as fellow members rally around you. (Once known as family.) It can also help get you in trouble, as with Bernie Madoff and his many club memberships.
NOTE: If you want to suggest changes to this or any other definition in our career dictionary, please feel free to add your suggestions in a comment.