What is flat surface raceway used to extend power across the surface of a floor called?

The term you are looking for is "Pancake raceway." This type of raceway is designed specifically for extending power across flat surfaces, such as floors, without requiring extensive modifications or installation of additional infrastructure. The name "pancake" reflects its low-profile design, allowing it to sit flush against surfaces, minimizing tripping hazards and maintaining aesthetics.

The other options refer to different types of raceways that serve specific functions or purposes. For instance, surface raceway generally refers to any raceway installed on the surface but does not denote the specific low-profile nature as effectively as the term "pancake." Flatter raceway is not a recognized term in this context, and while "power channel" could describe a raceway for power distribution, it is less commonly used than "pancake raceway" to describe the specific low-profile attribute needed for surface power extension. Thus, "pancake raceway" is the most precise and widely accepted term in the context of extending power across horizontal surfaces.