Social grades are a very simplified way of categorizing audiences by their class or income. This is very much a 'best fit' model and should not be considered a set rule. It is however a useful way of indicating a general gist of the type of audience member who may consume any given Media text.
Uses and Gratifications theory is a key theory in identifying what audience members feel they 'receive' from a Media text. In order to entice audience members into consuming a Media product, that audience member must feel they are getting something from it. This theory allows you to categorize this perceived gain,
Psychographics is a theory that allows you to categorize audience members by the way in which they think. It is a useful tool in identifying how to expressly target these individuals as, if you know how someone is thinking, it is easier to appeal to their interests.
It is theorised that audiences can take different levels of interest in a Media text, with active audiences constantly considering and interpreting details independently of the text, and passive audiences simply absorbing information as fact with little consideration to their own interpretation of this information.
This theory considers the different ways in which an audience member will respond during or following the consumption of a Media text. With some audiences interpreting a Media text in the way it was intended and others taking readings that can sometimes be entirely unexptected.
All screencasts below cover theory that is required for the A-level syllabus. If you are a GCSE student, feel free to have a go at learning about some. If you are able to understand and apply some of these, it will help you attain a Level 9. These are by no means essential learning though.