A significant movement in education concerns the use of open educational resources. By "open" it is generally meant that the resource is available at no cost to others for adaptation and reuse in different contexts. However, "open" is not a simple dichotomy; rather, there is a continuum of openness. We discuss four separate aspects of reuse and demonstrate how these describe different levels of openness. We discuss how the licensing and technical aspects of open educational resources affect the relative openness of an open educational resource. Implications for those creating open educational resources are discussed. (Contains 1 figure.)