It is just standard jargon, normally understood to mean that the end user is unable to do anything that will cause a problem to the software no matter how hard they try.
"Idiot proof" is the holy grail to all programmers. Often quite difficult to achieve.
To test how "idiot proof" a piece of software is, you would normally give it to a known idiot for them to make every possibly attempt to break it.
In my case I give my software packages to my boss (Director of Research and Eductaion, Head of Chemistry). Not the kind of person that you would normally call an idiot, but from the point of view of breaking software, he difinitely fits the bill.