is a specific kind of: unit, unit of measurement.

is a broader term that covers: sq in, square inch | sq ft, square foot | sq yd, square yard | centare, square meter, square metre | square mile | quarter section | acre | ar, are | hectare | arpent | b, barn | dessiatine | morgen | perch, pole, rod | em, em quad, mutton quad | agate line, line | column inch, inch ... show more.