Print resolution--what's it really mean?

I am new to 3D printing and am finding I may have to severely edit my designs which may be too optimistic for the printer's capabilities. I have been studying various printers specs and am confused by the resolution (typically Z axis) that has a wide range listed. For example, the ultimaker 2 has a layer resolution listed of 200 to 20 microns. What does that mean?

Is that the min/max that nozzle will be able to print and varies depending on how you select the finish of the object when sending it to the printer? Or does it vary by material being used--one material you can get expect a nice finish at 20 microns, but another will be chunkier at 175-200 microns? Or is it a total crap shoot and the expected performance of the printer could be anywhere from 20-200 depending on which way the wind blows, relative humidity, and alignment of planets?

Any insights appreciated.

Layer resolution is the thickness of the individual layers the printer can print.
Most fdm machines can easily handle a range between 0.1 and 0.4mm
I prefer mm to microns - just easier to visualise.

ie: 100 microns = 0.1mm

That's vertical layer resolution.
You also have horizontal resolution - which is mostly dependant on how large the orifice in the nozzle is.
I usually use a 0.4 or 0.5mm diameter nozzle. Which means that fine detail smaller than 0.4 or 0.5mm is no going to be great.
However horizontal resolution also depends on placemnt as well as nozzle diameter. So if there is room the printer does not always need to lay down a layer strictly in 0.4mm (standard nozzle size) beads.

You can increase horizontal resolution by using smaller nozzle diameters. Realistically 0.25m is about a small as it's easy to go, you can get 0.15mm nozzles as well - but by all accounts they are difficult to use. Watch this video: https://www.youtube.com/watch?v=LHg9phNSCEY

So theoretically you can print at 0.05mm layer height (have seen some fdm printers quote 0.02mm) and 0.25mm nozzle diameter on most current fdm printers.
Higher resolution printing takes a long time - watch the video :-)
After watching that I pretty much decided to not bother with the 0.15mm nozzle.
Unless I get another commission to make some more stupidly tiny things.
As an example of what is possible with a 0.4mm nozzle:
Attachment 11124

5 components for micro radio controlled figures. Yes that's a dime.
The black tyres are made from flexible rubber filament, the gears from colorfabb xt - pet-g and the brown motor mount from pla.
Everybody else told him you couldn't make things that small with fdm - I decided to try it :-)
Had i used a smaller nozzle diameter it would have been a lot easier :-)
Didn't occur to me at the time. :-)

And yes a lot does depend on the filament.
3d printing is as much an art form as a science. If you are easily frustrated - this is not for you :-)

Does that help ?

thanks that help me :)