Fog computing, a term popularized by Cisco and later the OpenFog Consortium, describes a distributed tier that sits between the device layer and the data center. Where edge computing usually means the device or its immediate gateway, fog nodes are typically routers, local servers or micro data centers that serve a building, a plant or a neighborhood and can coordinate with each other.
In practice the boundary between fog and edge is blurry and vendors use the words loosely. The useful distinction is architectural: fog adds a managed, networked middle layer that can run heavier analytics and buffer data for many devices, at the cost of another tier to secure and operate. Edge vs cloud vs fog compares the three.
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