**But I don't know what makes them slow burn. A romance which takes place over a long fic and they don't get together / make out until near the end? Is that what it means?**

Exactly! I'm not sure either, but I think that's what is generally considered as such. But how one keeps from said fic being hot and sweet and lovely and wonderful in all ways to being unbearably long and boring. I think it takes more skill and PATIENCE (I think it takes lot of patience, which I don't have either) to make the Slow Burn category.