There are a lot of businesses that offer the same products or services that you are offering. And people come in contact with advertisements from these companies all the time. So, why should people consider doing business with you and not your competitors? In other words, what unique will you be offering so that people do not go for your competitors? This ‘thing’ that your business is offering is your USP or unique selling proposition.
https://www.exnoweb.com/blog/how-to-make-advertisements-5-simple-tips-to-creating-an-effective-ad/