The subject and the operating environment are two terms that are close to analogous, but differentiated to some degree, as well. Effectively, we can think of the Environment as the absolute boundaries of the Subject. The Environment is the entirety of the data available to your Urbit – it is, you might imagine, the entire interior body of your Urbit up to and inclusive of its skin. In contrast, the Subject is the immediately focused-on and discussed portion of that corpus for the purpose of executing some code. Various levels of programs can be exposed to various delimited amounts of the operating Environment, as is necessary for their faithful execution.