Parked: A domain hosted by a middle-man for the sole purpose of generating revenue from pay-per-click advertising. Characterized by having no content of value.
This definition *might* work for NANOG, but my parking friends would disagree with the above.
If this is what you mean, then it is impossible to do so automatically. This definition requires determining the motiviation for the registration, which cannot be done by any technical means. For example, this definition would exclude a domain temporarily parked for a few months while a service is prepared and tested. If you mean determiming if a domain is likely to be parked or definitely has some other set of characteristics, it helps to work that out in precise detail. I'm not trying to be a pain, I'm genuinely trying to be helpful. For example, a commonly asked question is "how can I tell how much memory my program is using" and the canonical answer is "define what you mean by 'using memory' and the answer will be obvious (or at least you'll be on your way to getting it). (Physical memory? Virtual memory? Is the memory footprint of a shared library to be counted as 'used'? What if this is the only program that's using it? And so on.) DS