Creighton Broadhurst has posted his opinion of what Old School means to him on his blog, describing it mostly as about specific choices in Gameplay as well as Game & World Design. At the end he does mention a little something about rules systems, which is interesting as a lot of what he publishes for is Pathfinder, a game not typically associated with being part of the Old School approach, although he does declare his love for earlier editions of Dungeons & Dragons, and he is developing a product with Old School ideas for later rulesets called Gloamhold. Many of the elements he proposes are not exclusive nor unique to Old School games but they do typically tend to be among many of the definitions put forward by those who look at Old School play without locking things down to specific rules systems or games. There are of course some that are hallmarks, such as resource management and mapping which are heavy aspects of Old School play ( whether or not the mapper is the GM or not).
Of course, defining what is and isn’t Old School is one of those prompts that can turn conversations into arguments as people pitch their tents and choose positions about what is and isn’t Old School; on more than on occasion this has erupted across social networks as various factions weigh in on this topic.
Part of the reason that OSRToday doesn’t post a “definitive” definition (at least for the purpose of the site here) of what Old School is comes down to the fact that the issue is contentious, and OSRToday tends to err on the side of being inclusionary rather than exclusionary.