A programming model is what the programmer has to think about in order to write a program. Brainfuck probably has the simplest model I can think of - you have

A programming model is what the programmer has to think about in order to write a program. Brainfuck probably has the simplest model I can think of - you have an instruction pointer referring to the next byte in the program to execute, and a flat array of memory cells that program instructions may read and write. Every command in the language is about working with those two elements. C has a much more complex model consisting of statements that are stepped through, functions that may be called (including recursively) with parameters, local variables, global variables, static local variables, constness vs mutability, pointer types, names for symbolic access to those things... And probably a lot more that I've neglected. Concurrency is a thing that might be part of a programming model where you are allowed to interleave execution of multiple logical workflows but still write each logical workflow as a single unit of code. The programming model model tells you what properties you are guaranteed to get. An execution model is something that describes implementation of a programming model. A related example is how concurrency is implemented in a particular system. Is it multiple threads running simultaneously? Is it a complex state machine jumping between logical workflows as demanded by their semantics? Is it an even-more-complex m:n model involving both threads and state machines? Execution models aren't irrelevant to programming. They can have a significant impact on performance and edge-case behavior that the programming model doesn't clearly specify. But you should be able to write programs with only the programming model in mind and get correct code in most circumstances. (I'd call it a specification failure if you can't.) A programming model describes the tools the programmers have available, their semantics and interactions. An execution model describes how those things run on the hardware that is present.