While the values of the Open movement predate the internet, open educational resources did not come to exist, as such, until:
The internet existed
The non-profit organization Creative Commons had created six open licenses meant to be used for basically everything except computer software
Q: What the heck is an 'open license'?!
A: Copyright holders (like an author, for example) can license out the use of their creations to others - think of the author Steven King, licensing out the right to a movie studio to make a movie out of his next horror novel. (And you know he'll make them pay a lot to get that permission, too.) That's an example of how creators can make money from their 'intellectual property', and licenses are just that, legal tools.
Now, an open license is when a creator wants to let the Public know instantly that it's okay to use their work in certain ways - without having to ask them for permission, or pay money, etc. They literally put a visual representation of the open license on their work, a visual label that they add. Make no mistake, though - the actual license is a legal document, legalese and all (they can be found and read on the Creative Commons website).
Creators who use open licenses support the values of Open. Instead of reserving all their rights, they are voluntarily giving up one or more of their author's rights (aka their copyrights!) to the Public. The one right they never give up, though - is the right to be known as the creator of their work.
So...long story short, some people create
and add one of four Creative Commons licenses to it.
Q: Wait - you said there were six open licenses - why do they use only four, and not all six?
A: Two of those six Creative Commons open licenses don't give the Public permission to revise or remix the creator's work - and OER has to be able to be altered. So, people open-licensing OER can use any of the open licenses except those last two.
Q: So, OER needs to be alterable. Why would someone want to?
A: Say you're teaching a course....and you find a free online OER...you like most of it, but it's a little out of date, or you don't like the last two chapters, or you just wish you could add some additional material. The open license lets you do that...so you...make yourself a completely customized textbook.
Q: Sounds good. So then, you just take it and start using it....
A: Not so fast - you've created a new work (though containing bits of others' creation(s)...remember the bit about how the one right creators never give up is the right to be known as the creator of their work? When you use other's openly-licensed OER material, you need to do what is called attribution.( It's essentially the open licensing version of citing, though it's a little easier to do, there being only one format.) If you don't attribute properly, you are breaking copyright law.
Q: - !
A: Hey, the creator has voluntarily given up some of their author's rights - but not all - and certainly not the right to be acknowledged as the creator of that work. Open licenses are generous licenses - but not a free-for-all.
Q: Okay; so you attribute correctly, and you're good to go.
A: Well, you created a new work, though containing material from other peoples' openly-licensed works. Aren't you going to give it an open license?
Q: Oh...well...what if I don't want to give up any of my rights? Can I just keep it all rights reserved?
A: You actually might be able to do that - it really depends on what licenses the creators whose stuff you used, had used. Some of the Creative Commons licenses have the condition that anyone using their material to make their own new creation must use the same exact open license on the new work as they did on their material. Or-
Q: - you're breaking copyright law.
A: You got it! Or you could just not use that particular creator's stuff. Your wish to retain all your rights doesn't mean you get to infringe upon theirs.
Q: This open licensing stuff is getting really complicated.
A: Well, the Creative Commons (CC) folks wanted to give creators options - no one license fits all. The people who got together and created these (back around the turn of the century/millennium - 2000) are lawyers, after all.
Q: No kidding...
A: The fact remains, though, that there's plenty of openly-licensed educational material out there that you can mix together to make your own new work. Attribute properly, put one of the licenses on it that doesn't conflict with the ones on the materials you used, and start using it. It's free to your students, it's online so they have it from day one, and it's customized to your needs. Win-Win!
Q: Hmm. Okay, where can I learn more?
A: Here, in our entire guide about Open Educational Resources.