Someone who's small-minded has a narrow perspective or very firm, unchangeable opinions on things. It's almost impossible to get a small-minded voter to change his or her mind.
If you're small-minded, you have a biased view of the world, and you're probably not very tolerant of those with different opinions or experiences. It's as if small-minded people can't step outside their own perspective to empathize with others. A small-minded governor might want to keep all immigrants out of his state, and someone with a small-minded focus on money won't understand your dream of being a poet.