PT: Primitive token. A special token that has the syntax of an identifier (i.e. if it wasn't special, it would be treated as an identifier) but executes a special operation that (for the most part) cannot be accomplished by other means.
Nametable: A key-value mapping structure (compare to Java's & JavaScript's Map, python's dict) that is the second most important data structure of SOF internally after the Stack. All Nametables live on the Stack.
GNT: Global nametable. Lowest element on the stack, used for top-level lookups and globaldef. Exported functions keep the GNT at export time.