I don't know what the designation expands to, but I've looked at a board and they are just shorted links. They have the footprint of a SMD resistor, but are shorted down the center, and no component is placed. In theory the short could be cut out, and replaced with a resistor - perhaps for troubleshooting by isolating, or for inserting a small resistance for signal integrity reasons.
I'm looking at the schematics for the MiniZed from:
There are symbols that look like resistors that have reference designators "NTR[1:16]". I'm curious as to what these mean? They aren't in the BOM, so they don't seem to be physical components. I haven't been able to find a general "reference designator" list which gives meaning to "NT" or "NTR".
Mostly they seem to bridge two nets of different names, which okay, this could be a way to "properly" do that or get around DRC errors/warnings. But this is not always the case, see NTR14/15/16. So... What are these?