People place used household items, clothes, etc. in their yard and offer them for sale. Usually held on a week end, a "yard sale" often involves one, or a few families who pool their unwanted items to sell, often very cheaply.
Parallel term: "Yard saliing." To drive about from yard sale to yard sale.
I bought this sweater at a yard sale for a dollar and a half.
The Jones family are having their yard sale next week/