Science is, simply put, the study of the world. It is a way that people try to better understand the world around them. It's true that most of science is theoretical, but it's not just someone sitting in a room thinking "hey, this is a really cool idea... THEORY!!!". For something to be considered a theory even, it has to be tested and proven to be beyond just that of a hypothesis. Even if it's not totally proven, it still has some fact in it, whether mathematical or otherwise.
The vast majority of religion is mainly belief with a sprinkling of historical fact. True that most religions have deep roots in mysticism, rumor, manipulation by storytellers, and superstition, but most religions (major religions at least) have at least some truth behind them. There is historical proof that a man named Jesus lived at the time or around the time specified for the prophet/savior/man (depending on your beliefs) Jesus Christ to have taught and lived... the Buddha was a real living person as well. When people believe a religion, it's not them being an idiot. Some people really need something solid to hold on to, especially with the way the world is today. And truly, nobody can tell if a religion is true or not. I am personally a Roman Catholic, though i don't believe everything taught to me... this being that some teachers explained one thing as a truth, while others stated it to be totally ficticious. Regardless, religion can never be proven, because the basis of a religion is belief. If a religion is ever to be truly "proven" then it would cease being a religion and become a science. Hence, what Mariella said. I mean, alchemy was a true science for some time, until it was disproven as mysticism and whatnot. (though wouldn't the ability to transmutate physical objects from one state to another be awesome? u_u sorry, opinion :3 ) Therefore, i think at least, the major difference between science and religion is;
Religion is proven only by belief, and Science is believed only with proof.
buuuut, that's just my thoughts on it.