The Primary Representation System is the representation system that a person favours most when forming and holding their model of the world.
For example, someone with a Primary Representation System of Visual will tend to use Visual predicates more frequently in their language — words like see, look, clear, picture and bright.
The Primary Representation System is also the system a person defaults to in moments of high stress — it is the most deeply habitual channel through which they process experience.
Understanding a person's Primary Representation System allows you to communicate in the language that resonates most naturally with how they think and feel.
See also: What are the Representation Systems? | List of Predicates | What is NLP?