Are the terms "Sheet Resistance" and "Sheet Resistivity" interchangeable?
Both of your links give the resistivity or resistance in the correct units of ohms per square.
The bulk ink will have a volume resistivity given in ohms/metre. When printed at a specific thickness into a sheet, the sheet resistivity is then given in ohms/square.
It should be obvious with a little thought, and the way series and parallel resistances combine, that an area of film two squares long and two squares wide has the same resistance from side to side as a single square.
If you take a trace that is 10 times as long as it is wide, it will have a resistance of 10 times the ohms/square of the film.