If some consensus is reached that it’s confusing, I can change that, if a good alternative is proposed. However, it’s normal in any technical documentation or any other non-fiction prose, or actually in all produced human language, that you can add additional qualifications to words to disambiguate. There’s not just one word, there are two phrases: “grid pitch” and “pad pitch”. They are clearly two different things, at least for me.
NOTICE: what I say next should be true for KiCad future version 5. I remember seeing situations where mouse movement didn’t snap to the currently selected grid, but I don’t remember if it was in v4 or in some nightly builds.
I don’t understand. There’s only one active grid in pcbnew, the one selected. There are possible preselected values and then the possibility to define the values precisely yourself. Only one of the possible grids are selected at one time. The grid values you defined manually yourself is called “user grid”. The currently selected grid is the grid where the cursor snaps to. I doesn’t affect the items which were positioned or edited before the current grid was selected. It’s effective when you move or edit items with mouse (or with keyboard arrow keys in WYSIWYG manner). Then the movement of the item snaps to the current grid.
But not everything hits the current grid. The internal coordinate system of pcbnew is based on nanometers. That’s the absolute smallest defined distance of two things in KiCad. Anything can be set to that coordinate system e.g. with the Properties dialog of an item, regardless of the current or previous or future grid. Is this the other grid you’re referring to? If something is imported from e.g. other software, it must be fit to this internal coordinate system. If the other software had smaller coordinate system “pitch” (the smallest value between two defined points), the imported coordinates must be rounded to the nearest nanometer value. If the other coordinate system “pitch” was more coarse, the values will fit without conversion.
As far as I know, the pcbnew coordinate system’s smallest possible distance is never referred to as “pitch”, and the absolute fixed coordinate system isn’t reffered to as “grid”, but I may be wrong.