It's sort of like a set - with a bunch of contributors. Sets are groups of photos with a common theme. Groups are groups of users who have a common interest and who include some of their individual photos into the group "pool". There are 3 kinds of groups:
- Public - anyone can join
- Public, invite only - anyone can view the group's pool of pics, but only those with invites can join
- Private - joining and viewing are both done by invitation only
Finding and Joining Groups
Go to http://www.flickr.com/groups/ to find a search box that will allow you to find groups fitting your interests. When you find a group you would like to join in the results list, click on the name of the group to go to its page. There, if the group is public, you will be able to join it by clicking on the link that says, "Join This Group?". Confirm that you really want to join, and you are in.
Adding a photo to a group
To add a photo to a group to which you belong, go to that photo's page and click on the "Add To Group" button at the top of the photo. A list of groups will appear. Click on the name of the group and your image will be included in that group's photo pool.
Other uses for Groups
Groups also allow the members of the group to engage in discussions about their interests, find people in the group with similar interests to their own and feel like they are part of a community on Flickr.