A function pointer is the mechanism by which you realise a callback.
For me, a callback, is when you have two modules and the function pointer is used to call back the functionality from the calling module in an environment and at a time determined by the called module.
A polymorphic method is a callback used in a certain way in context of OOP. You have a callback from one module (the implementation) passed to another module that can call potentially many different implementations through the same interface (which makes it polymorphic). This callback is tied to the structure by the calling module, which makes it a method. You may have language support and have entire mechanism hidden from you, but this is essentially what is happening. A pointer to function that is passed to another module for execution.
Now, when you do "manual" OOP in C without building your own vtable macros and such, I think "polymorphic method" is a bit too much and "callback" is more fitting.
For me, a callback, is when you have two modules and the function pointer is used to call back the functionality from the calling module in an environment and at a time determined by the called module.
A polymorphic method is a callback used in a certain way in context of OOP. You have a callback from one module (the implementation) passed to another module that can call potentially many different implementations through the same interface (which makes it polymorphic). This callback is tied to the structure by the calling module, which makes it a method. You may have language support and have entire mechanism hidden from you, but this is essentially what is happening. A pointer to function that is passed to another module for execution.
Now, when you do "manual" OOP in C without building your own vtable macros and such, I think "polymorphic method" is a bit too much and "callback" is more fitting.