A level category refers to a type of level. Examples of level categories are: video, audio, text, alarm, and time code. A level category can contain multiple levels.
A level is a specific instance of a given level category. For example, a video level category could have five different levels. Each of these five levels refers to a different type of video level within the video level category.
A channel refers to a group of physical assignments. A channel is made up of several physical assignments. Each assignment is associated with one level.