A unique selling proposition is the one factor that (according to a company) distinguishes its product from those of its competitors. The unique selling proposition should become the main focal point of the company's advertising strategy.
If you think about various companies that run ads on US TV, you should be able to understand what they each see as their USP. For example, it is clear that Southwest Airlines seeks to distinguish itself based on its lack of hidden fees. McDonald's tries to market itself as a family-friendly company where people can have a fun experience. These companies are presenting these qualities as their unique selling propositions because they feel that those qualities differentiate them from the competition.