A Meetup is a group of people with common interests that schedule meetings to discuss their topic of common interest. The Meetup.com website facilitates finding groups of interest, administering group membership and posting upcoming events.
Basically, the Meetup structure is a social media network that allows individuals to connect with other individuals in their area. Each group is self-administered and meets locally. Individual group leaders register a group of interest and solicit their friends to form the core group. Word of mouth and self-promotion are normally the means utilized to get new members to join.
Topics of interest for Meetup groups vary widely by location. I live in the Raleigh, NC area and obviously have a strong interest in web site development, search engine optimization, and project management. Local Meetup groups exist for each of these topic areas. After I register as a Meetup user, I can request membership in any group listed. Once approved by the group leader I will receive all upcoming meeting announcements and events. I RSVP to any meeting that I am planning on attending.
Meetups are a valuable resource to learn more about your areas of interest and to share what you know with others. The group depends upon members sharing with each other. Give it a try!