A non-excludable good is a good whereby it is not possible to exclude people from using the good, thereby making it difficult to restrict access to the good based on price.
Alternative explanations for apparent non-excludable goods
Some goods which we claim are non-excludable are not really non-excludable, in the sense that, at a certain cost, access to these goods can be restricted.
Access fees and walling
Public parks, roads, and public infrastructure are sometimes viewed as non-excludable. However, public parks can charge an entry fee or restrict access based on other criteria by fencing themselves, and roads can operate on usage or toll taxes for pedestrian and motor traffic.
Bundling with other excludable goods
Many goods which we claim are non-excludable are in fact accessible only to people within a certain geographical region, and hence, access to these is restricted to people in that geographical area. Thus, it is possible for those who own property rights to that geographical area to bundle it along with the rights to access to that geographical area. For instance, various public goods that are accessible within a walled community can be paid for through the rents or fees for living in that area.