An interp is the short form of interpreter.
It's the thing that communicates to you and me, that explains my thoughts to you, it is any kind of transition device.
In the case of you right now, you are my interp, as you are seeing dots on your screen and interpreting it into thinks.
It's a beautiful thing. There isn't any fundamental difference between a compiler and an interpreter, they both do the transmogrification of thinks except that a compiler does it all at once and an interp is more fluid, its more adaptive, it runs with you as you think.