GNU poke is a pretty new program and it introduces many a new concept. As people are starting to join the development, I think it is a good idea to clarify how I call things. The idea is for everyone to use the same nomenclature when referring to pokeish thingies. Otherwise its gonna get very confusing very soon!
First of all we have poke, the program. Since "poke" is a common English word, when the context is not clear we either use the full denomination GNU poke, or quote the word using some other mean.
Then we have Poke, with upper case P, which is the name of the domain-specific programming language implemented by poke, the program.
This distinction is important. For example, when people talk about "poke programmers" they refer to the group of people hacking GNU poke. When they talk about "Poke programmers" they refer to the people who use the Poke programming language.
Finally, a pickle is a Poke source file containing definitions of types, variables, functions, etc, that conceptually apply to some definite domain. For example, elf.pk is a pickle that provides facilities to poke ELF object files. Pickles are not necessarily related to file formats: a set of functions to work with bit patterns, for example, could be implemented in a pickle bitpatterns.pk.
I hope this helps to clarify things.
Happy poking! :)