Surface resistivity is measured in Ohms per square (Ohm/). Ohms are units of resistance, but what about the square?

Engineers know that you can measure surface resistivity from one point on the surface to another using an ordinary ohm-meter. Then the units would be Ohms per distance between points or Ohm/m. But this method yields very inconsistent results, especially with surfaces that are not perfectly homogeneous.
More consistent results are obtained by measuring the surface resistivity between two bars. For simplicity, two parallel bars of equal length are placed exactly 1 length apart on the surface to be measured. They form two opposite side of a square. It doesn’t matter how long the bars are, since longer bars will be placed proportionally further apart. The resistance measured between the two bars in Ohms is the resistivity of the surface in Ohms per square!