State

State is whatever can change as a function of some notion of Time, whether ExecutionTime or WallClockTime.

A Process may have DiegeticState which is explicitly represented in the Program and manipulated by the process. Processes also have NonDiegeticState (such as the instruction pointer) which is not explicitly represented and can't be reflected on by the program (because such reflection would necessarily change the very state it is trying to observe).

Within a Process, state resides in Variables. State can be ProcessGlobalState, meaning its variables retain their values and can be Accessed for the entire lifetime of the process, or it can be LocalState, which only remains accessible for some portion of a process's life.

LocalState may reside on the CallStack, or in Closures on TheHeap. Heap storage is more difficult to formalize and reason about, as evidenced by the intricacies of garbage collectors and the sprawling discussion on the Routine page.

State also exists outside the process, and this type of state can be accessed via SystemCalls. I consider this type of state to be different from ProcessGlobalState, since all possible changes to the latter can be grokked by inspecting the program, while changes to process-external state cannot be predicted by inspecting the program.