Quantum tunneling refers to the quantum mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount.
Which, if you understand anything about physics, makes you go 'huh?'
It's like how some particles want to be somewhere in the world, and they go on a bear hunt...because if they can't go around it, they just go through it! ^_^
I had a lot of fun learning about something so fascinating and different. This video was a good intro to it. (Though I read a lot more about wave particles than I ever though I would!)