An uneducated or ignorant person.
Origin of the word
In Ancient Greece idiot meant a person who didn't take part in the Direct democracy that many Greek city states used. This was and is idiotic because people living in Democracratic nations who don't take part in their government risk the government ignoring their interests. In Representative democracies too there are far too many groups of people who complain that the government ignores their interests but don't bother to vote. 
- Unfortunately many Conservatives do go out and vote in ignorant or selfish ways.