All three of the terms open, educational and resource seem to be difficult to define to anyone's satisfaction. I believe this is because to a certain extent all three of these terms have a different meaning to everyone
What does it mean to be open?
What does it mean to say something is educational?This question always leads to the formal verses informal education debate. It is not really fair to say that only things created at an educational institution or with the purpose of education are educational. Informal learning occurs all the time and because it is personally relevant may have more of an impact on the learner. My definition of education is any situation from which a person learns. This is probably way to broad for the purposes of defining an OER, but I do think it is something which is personal and should not be confined to formal learning.
What is a resource?
I don't really want to limit resources to tools or digital assets. I think resources can include people, places (eg. a library) and things. I was wondering if an experience could also be a resource, but I think a resource might need to be more solid. A picture of an experience could be a resource because it is something tangible you could refer to again. My definition of a resource would be an object or asset which can be used for a particular purpose. The resource would not have to be created with learning in mind in order for it to be educational though.
My definition of an OER
According to what I have written above an OER must be an easily available, freely usable and customizable object or asset which can be used formally or informally to learn. I view the open part of the definition to be most crucial however. If something is open on all three of the levels discussed in the Tuomi article it wouldn't matter if it was intended to be educational or a resource. It could still be viewed as an OER by the user as long as they had open access to it.