There are 3 notification categories: Thread, Forum and Global. Let's explain each one of them: Thread: The notification options of this category will only affect the current thread. A thread is all the posts of a single topic. For example, in the following image, the topic is called "In the Name of the Father". Thread name All the posts inside this topic are called a Thread. The notifications options of the Thread categories will only affect the posts inside the topic "In The Name of the Father". Forum: The notifications options ot this category will affect all the threads inside the current forum. In our example, the forum is Drama Movies. According to this, setting notifications options in the Forum category will affect all the posts inside the forum called Drama Movies. Global: The notification options of this category will affect all the posts regardless of in what forum they were posted to.