You would have to read Proudhoun an Anarchism to understand what is meant by the saying. By "property", Proudhon referred to a concept regarding land property

You would have to read Proudhoun an Anarchism to understand what is meant by the saying. By "property", Proudhon referred to a concept regarding land property that originated in Roman law: the sovereign right of property, the right of the proprietor to do with his property as he pleases, "to use and [to] abuse," so long as in the end he submits to state-sanctioned title. Proudhon contrasts the supposed right of property with the rights (which he considered valid) of liberty, equality, and security. Proudhon was clear that his opposition to property did not extend to exclusive possession of labor-made wealth.