Depth Of Field, it's the amount of the picture that is in focus. So in this pic the can is nicely in focus, with the background and foreground out of focus, so there is a small (narrow) depth of field. DOF can be used to isolate a subject within a frame, as you have done here, I'm guessing by accident!
Ahh yeah I know what Depth of field is, or appature, as it's known! I wanted the can to be in focus, and not much else, so yeah it was on purpose!
Just never heard it referred to as DOF- my bad!