The concept behind a 365 Challenge is to take (and share via a photo-blog) 365 photos during the year. Participants in the challenge are encouraged to visit other blogs and post comments. It’s a great way to get compliments, feedback and constructive tips on your photos and make some online friends as well. I've been told that interaction with other photographers and the quest to match themes and take 365 photos can be very motivating.
There is a list of 365 themes to provide inspiration. Photos should relate to one of the given themes, however an extra 52 “wild-card” options have been provided to for any of the predetermined themes.