Do you know the difference between multiple submissions and simultaneous submissions? Though some people use the words interchangeably, there is a difference between the terms. In the case of a multiple submission, a writer sends several different manuscripts to one editor. In other words, an editor may end up with two or more pieces from one writer. Conversely, a simultaneous submission is when a writer sends the same manuscript to different editors. This means that your story is being considered by more than one editor.
It's important to understand the difference and know if multiple or simultaneous submissions are accepted. Your work might get rejected if you send an editor multiple submissions when the guidelines state otherwise. So it's your job to find out if what is permitted.
For instance, Kid's Imagination Train has a small staff so we don't accept multiple submissions or simultaneous submissions and we state that in our guidelines. But that doesn't mean that everyone adheres to the rule. Once, a writer sent a very nice poem which was accepted for publication in KIT. Since the piece required a little editing, I worked on the revision for a few days. And then, the author retracted the poem. The explanation: another publication had excepted the piece. The author had submitted her work simultaneously. I was not a happy editor—my time was spent editing a piece that KIT will not be able to use.
Be sure to find out what an editor prefers before submitting. If multiple and/or simultaneous submissions are permitted, you will get the chance to have your work and lots of it considered by editors. But when the guidelines state that an editor does not want multiple or simultaneous submissions, then follow those requirements. That way, you will know exactly what to submit and how to target editors who may be interested in publishing your work.