Active coils are within the spring. An inactive coil is at the end of the spring on each side, therefore, active coils are all of the coils that aren’t on the ends of a spring. If the spring has an open end, meaning the coil at the end is cut in half, that means it has a half inactive coil.
When dealing with the language of springs, if you need to count the amount of active coils, just start on the second coil and work your way to the second to the top/bottom coil. You will be able to communicate really well with a spring specialist.