Desert Flame is what Greek Fire is called on Orr.
Just like its Earth namesake, Desert Flame refers to a multitude of weapons. The all hing around the simple idea that if you heat something up and throw it at someone, it will burn them. Or burn things around them.
"Let's all be honest here. Fire is fun. What's more Fun? Watching your enemies try and put out a fire that's hard to put out. Even better, seeing it spread when they throw water on it. It's a great weapon that allows you once your job is done to sit back and enjoy the show. " - unknown
This article was created to be linked to explain what this is.