p(0) - Puppet Language Level Zero
The point of the p(0) is that it can be easily written and parsed in non-Ruby languages without any Puppet dependencies, just like JSON (although admittedly more difficult than JSON). It is both a language spec and an implementation of that spec in as many languages as possible. It is also expected that some or all of those implementations will move into separate projects, such as ruby gems and python eggs.
p(0) is effectively a simplified graph language, with Puppet Resources being the nodes and dependencies being the edges.