An open educational resource (OER) is content that is ‘libre’ (openly-licensed content) and at the same time ‘gratis’ (free of charge).
An OER need to carry a visible open license, such as a Creative Commons one, or an explicit acknowledgment that the educational resource is free of charge and free to be used, shared, remixed, adapted, distributed etc.
There are different types of OER (e.g. fully licensed or licensed with restrictions, depending on the type open license chosen).
Content in the public domain is also considered OER.
One of the benefits of using an OER for teaching and learning is that it reduces the possibilities of users infringing copyright.
At the same time, it grants greater permissions in the use of content, such as adaptation, translation, remix, reuse and redistribution, depending on the type of license applied to the content.
OER can have different granularity, varying from a learning object (e.g. a picture with a specific teaching purpose) to a full course (e.g. a MOOC or an open - libre and gratis - online course).
Source: OpenEdu Framework, 2016