Method is one of the four basic grabs in snowboarding and skateboarding, the other three being indy, mute, and melon. To grab method, all you have to do is grab the heelside of the board with your leading hand. This makes it one of the easiest of the four.
It is also the natural grab used for backside airs, and thus, when someone performs a backside air with a method, calling it a backside method is somewhat redundant. If you use the term backside method in normal conversation or description, you probably won't receive any criticism.
However, if you are working for a well-known magazine or website, and mistakenly use the term backside method (or frontside indy, for that matter), you will promptly receive a shitload of letters and emails declaring you incompetent. This has happened to contributors to both monsterskate.com and Thrasher magazine.