Core Files
The grouping of low level files that support an embedded processors base firmware environment. A core is typically composed of source (.c) files, header (.h) files, and a C++ (.cpp) file.
Shield
A module that plugs into the headers of a device like the Arduino. This module typically adds a unique ability to the base device such as motor controls, wireless communication, prototyping or even an OLED.
Backpack
A module that attaches to the back of a device like the Arduino. This module typically adds a unique support feature to the base device.
Module
A device that has a unique functionality and is easily attached to other devices to expand the functionality and features of the base unit. An example of this is a mouse (module) can attach to a computer (base unit).
Compiler
A program (computer application) that translates code written at a high level to a more basic low level code. A typical application of this is code written in C++ (easy language for humans to understand) getting compiled (translated) into Assembly (an efficient language to upload to an embedded controller).
Processor Core
The base of the processing unit usually defined by the operation size (bits), processing speed (MHz), program memory size (KB) and the amount of flash memory (KB).