I'd suggest listing it as something like, "Additional graduate level coursework" and list the dates you were in the program and courses taken (and passed) in a block paragraph. You don't want take a lot of space with it, but show them you didn't have a big gap of time you were doing nothing.
Be prepared to explain why you left graduate school if asked about it on an interview. Though, if that coursework isn't required for the position, they may not care whether you were in a matriculated program and left or if you were just taking some extra classes as a non-matriculated student.
Of course, if you failed all those courses, I don't know how to handle it, because if they ask for a transcript, you're really screwed. I'd perhaps only list ones you passed, since a course that's been failed really doesn't add much to your knowledge. If you left for other reasons, that's easier to explain, such as financial considerations, family obligations. As long as they aren't ongoing problems that would leave an employer wondering if you'd stay with them too...for example, if you needed to move closer to home to care for an ailing parent, and the new job is close to home, that would make sense to an employer. Likewise, someone who left graduate school to have a baby and raise it until it was school aged, and now returning to work once the kid is in school would be a "safe" reason, as long as it was clear you weren't planning on getting pregnant again very soon and leaving to do it all over again (but an employer isn't legally allowed to ask if a woman is planning to get pregnant or have kids during the interview, so if this in any way applies, don't even mention it since they CAN follow up if you bring it up as part of the discussion). BTW, I have no idea of whether you're male or female, which is why I'm bringing up this point.