Film Format Basis vs. Pixel Basis
The depth of field (DoF) is the region in which, due to optical physics, a point has, on the film or the sensor, an image smaller than the size of the circle of confusion (CoC).
The CoC is "classically" determined from the accuracy of the human eye and the distance at which a given size image will be looked at, a common assumption is that the viewer will be at a distance equal to the diagonal of the image. This is the approach of the film format based DoF, taken by lens manufacturers even Fujifilm takes this path for Fujifilm X lens and DoF calculators. The CoC standard value for a full frame 24/36mm film is set to 0.03mm, and the equivalent CoC for a Fujifilm APS-C size is 0.02mm.
But, in a digital camera, you can also have the other approach, you could set the CoC to get the maximum use of your sensor taking in account its pixel size. This is the path Fujifilm takes when it calibrates the CoC for the viewers DoF indicator at 0.007mm
On its latest camera X-Pro2 and X-T2, Fujifilm gives you the option to choose one or the other value : "Film Format Basis" / "Pixel Basis"