The beltway term for those supporting Trump is "low-information voters" who arent really paying that much attention but have heard of him and like some of the simple things he says like how he can solve the gas prices thing with a phone call to OPEC and taking over some oil fields...because it really is that simple!
Yes, it's largely low information voters, but it's a particular subset of low information voters. Not exactly "the far right", as some have suggested. More of a fusion between the more populist/xenophobic elements of the "center" (so to speak)--the type who might have once voted for Ross Perot--with elements of "the far right". I mean, Trump recently blasted Paul Ryan for his Medicare cuts and has proposed imposing 25% tariffs on goods from China, so he's not exactly championing free market capitalism.
