Whereas a buyer persona is a representation of your ideal customer, a negative -- or "exclusionary" -- persona is a representation of who you don't want as a customer.

For example, this could include professionals who are too advanced for your product or service, students who are only engaging with your content for research/knowledge, or potential customers who are just too expensive to acquire (because of a low average sale price, their propensity to churn, or their unlikeliness to purchase again from your company).