Ah. So court challenges to out of control agencies like the IRS, ATF, and EPA have a chance at being more sucessful.Basically, this ruling means that the various federal agencies cannot make up regulations out of thin air but must limit themselves to the definitions set up in the laws that create the regulatory authority. "Chevron deference" was the older test that leaned in favor of the agency in a disputed regulation. It was not even used in this case, meaning that the court is willing to go to the original meaning and intent of regulatory law instead of the derived meaning by the bureaucrats.
It will not have an immediate effect of reigning in such regulations but should mean that challenges based on the original law have a better chance of succeeding.