These terms, and others, do seem very similar. They’re named from a conceptual standpoint, and so could be defined as follows:
- A “framework” is a “foundation” or “support structure” around which you build your actual application. The .NET Framework includes not only a foundation (the CLR) but a series of libraries that provide standardized functionality that you would otherwise have to implement yourself. Other frameworks or foundations provide more specific areas of support, such as in UI, data storage, client-server interaction, etc. Frameworks provide a relatively static, generic structure on and in which you build something specific and unique.
- An “engine” is a self-contained, but externally-controllable, piece of code that encapsulates powerful logic designed to perform a specific type of work. Engines exist to do “heavy lifting”, where you instruct it to perform some complex, abstract task, and it handles the specifics in a relatively efficient manner without further external guidance. SQL implementations, and other services that perform searching, are typically called “engines”. There are also physics engines, graphics engines, etc., which all have in common the idea that you tell it “do this” in some generic manner, and it handles the details.