eBird is an online database that accumulates observations of birds (including location, date, time of day, number of individuals, and info about age, sex, and behavior and media such as photos and sound recordings). I believe its goal and reason for existence is at least twofold: users have a place to keep records of what they have seen and scientists can use the records to map ranges, determine movements of birds etc.
I learned about eBird in 2006 at a local Audubon Society meeting and opened an account shortly after following the directions on the website. From then on, whenever I went birding, I would keep notes of birds seen and then create a list on eBird on my computer when I got home. I also added records from handwritten lists I had made before 2006. When the mobile app came out, I began to use it to record birds while out birding. I now have more than 3500 eBird lists. When I report a “rare” bird on eBird, a volunteer eBird reviewer will check to see if I have provided adequate documentation of the bird (a photo, sound recording, or written description that shows how I eliminated the more expected species).
I believe eBird is beneficial to me (record-keeping and review of rare birds by “expert”) and I hope it is also beneficial to science and conservation.