Not all freely accessible materials on the internet can be considered OER. Although there is some variation across different definitions of OER (see the Table below), if you are not permitted to freely access, adapt, and republish an online resource, these materials cannot be considered to be OER.
Simply having free access to a resource on the internet does not grant you the permission to revise, remix, or redistribute it. A good example of this is MOOC content from companies such as Coursera, which are usually free to access but copyrighted, with no rights granted to the user to revise, remix, or redistribute the content. Even in cases in which you obtain the permission of the copyright holder to reuse, link to, or embed free materials for educational purposes, these materials would still not qualify as OER.
Image Source (CC-BY)
OER, free, internet, materials, remix, redistribute, republication, link, embed