In print publishing it is called, Serial Rights, when you sell an article to a print magazine in, say, the UK, you are selling: First British Serial Rights. That means the publisher can print the piece in one edition in the area covered by SR. You are free to sell that on to publishers in other countries, and still command, First, say, Nigerian, or, USA, serial rights, although sometimes, often, you sell First English Language Serial Rights.
You are also free to sell on to competing publications, at a reduced fee, Second British Serial Rights, the chances of doing so are remote, competing publishers tend know what each other is doing. You can sell SBSR to non-competing publications, although it is always better to re-jig the piece for the readership of the new submission and sell FBSR:-)
The same system applies to electronic rights, re-jig your articles so that you don't spread the same thing around. As long as you haven't given away your copyright, you can do what you want with your work.