What does "no fit" mean in electronics?
This must be British.  For them "fit" means something like what we would call "install".  For us, "fit" means how well something fits, meaning how good it is at mechanically going into the right mounting holes or whatever, or how effective it is overall in the role it is being used in.

In this case "no-fit" means "do not install".  This is often done when a part may be useful for original testing in the lab.  Once the product has been verified, the part is of no use anymore.  Instead of respinning the PCB, you leave the pads there but just not install the part during manufacturing.

The same PCB can be used to build different variants of a product depending on which parts are installed or not.  In one case I had a product that was to be sold with either a RS-232 or CAN interface.  Since space was tight, I re-used the PCB area for the CAN driver chip and the RS-232 chip.  The pads of the two chips sortof overlapped such that only one could be installed at a time.  There were some other parts that had to be installed or not depending on the variant being built.