What is synthetic marijuana?

Synthetic Marijuana is created in labs, it all has to do with biochemistry and taking genes from a certain plant and growing it the way they want it to grow. It's like a test tube baby, nowadays you can pick the eye color and hair color and such of your baby based on your genes. They do this with Marijuana in labs to get rid of impurities and make them more potent. Of course I don't think this is widely done, and since it is illegal to sell, I'm sure there aren't any street dealer making synthetic marijuana.