My understanding was that, in the US, "Malt Liquor" applied to any beer that had an alcohol content above 5% regardless of what market it was aimed towards.

The term malt liquor definitely has connotations of cheap, poorly made beverages consumed only for the effect of the alcohol, but I've had many high quality beers that technically fit the malt liquor label.

Feel free to correct me on my above assumptions, I'll admit I'm not 100% clear on US liquor laws