The Discussion Board feature is used as a communication tool for posting and responding to messages. The Discussion Board is used asynchronously; which means that users in a course do not have to be logged on to the course at the same time to communicate.
Forums are made up of individual discussion threads that can be organized around a particular subject. Create Forums to organize discussions.
Threads are a series of posts related to a similar topic. When creating a Forum, the Instructor has the option of allowing or not allowing users to start threads.