A positioning statement summarizes why you are the best choice for your ideal customer.
This is an internal statement, meaning that your customer will never see it. But it's helpful to have for yourself to reflect on, and it's helpful to have if you have any employees that come on board and need to understand your relationship to your customers quickly.
In an oversaturated market (such as ours), a positioning statement is a really great thing to have because it also focuses on the things that make your business special and unique (compared to your competitors/peers).
The basic framework of a positioning statement is as follows:
In the eyes of [ideal customer], [your brand] is the best/only [frame of reference/USP (unique selling proposition)] because of [reasons to believe].
As an example, here's a positioning statement that I wrote for a client who designs luxury kitchens:
In the eyes of the professional mom, Wolfgang Studio is the only kitchen design studio in Des Moines that offers custom cabinetry because of their attention to detail, their knowledge of up-to-date trends, and their vast experience in the industry.