The editor is the program that you use to build things, to put all the things together that your game consists of (images, sprites, sounds, scripts etc). This baby:
The engine is a separate program that takes everything that you have built in the editor and runs it on your computer, the web or mobile device.
This is the engine running the data that I have created in the editor above:
The editor contains a copy of the engine that the editor uses to run your game when you select Project > Build from the menu.