resize - Gimp : difference between crop and canvas size

I would like to know the difference between the crop tool and changing canvas size.

If I reduce the size of the canvas, a yellow dashed line stays around the previous size. On the other hand, when I crop an image, the yellow dashed line follows.

What is the difference between resizing the canvas and cropping an image?

Answer

When you make your Canvas smaller you are allowing for larger layers around the Canvas, you are just saying: "this is the area of my image that I want to show". When you crop, you crop all the layers, ie: you delete everything outsize the cropping area.