Difference Between Target Audience And Persona - Market Update

The difference between two things is the way in which they are unlike each other. the degree to which one person or thing differs from another: [countable; usually singular] The difference in their ages is about six months. [uncountable] There isn't much difference between one politician and another.

You must have known some marketing campaigns that fell off due to a lack of connection with the target audience. Also, maybe they weren't clear about or didn't know their ideal customers.