The term fog computing (or fogging) was coined by Cisco in 2014, so it is new for the general public. Fog and cloud computing are interconnected. In nature, fog is closer to the earth than clouds; in the technological world, it is just the same, fog is closer to end-users, bringing cloud capabilities down to the ground.
The main difference between fog computing and cloud computing is that the cloud is a centralized system, while the fog is a distributed decentralized infrastructure.