What is the definition of a 'core' physician?

On April 30th, I conducted a webinar for Palomar Medical, Inc. on the topic of optimizing Local Search Engine Optimization tactics to boost your practice on local internet placement and ranking. Soon after the webinar, I was contacted by many physicians with many questions. I felt confident in answering all of them, except for one. And, that question was "what is the definition of a "core" physician"?

I was stumped.

I've searched the Internet for a documented answer and found none. I then perused quite a few physician's websites where it was clearly stated they were "core" physicians. It was also clearly stated that those medical specialties that were not deemed as being "core" were not qualified to perform certain aesthetic procedures. Not to be accused of being "flippant" by a physician as in one of my previous posts, I had thought that it was experience, training and number of successful procedures performed that made a physician "core" in that particular aesthetic modality?

Even on review and educational websites such as RealSelf, all non-"core" specialties were removed.

The answer I received from RealSelf stated : "RealSelf is no longer hosting profiles for participants who do not meet specialty designation criteria set forth by updated RealSelf policies. We have encountered problems with doctors and other medical personnel answering questions far outside their expertise or specialty and, in some cases, even dispensing inappropriate and dangerous advice to our readers. The aforementioned changes have been implemented in an effort to prevent these situations from arising."

Not to elicit any aggressive comments here, and I mean no disrespect to any medical specialty in particular, I just would like to be enlightened as to where the definition of "core" was derived from and what medical specialties that includes?