The rod is a unit of length in the imperial and US sytem and uses the symbol rod.
A rod (or perch, pole, lug) is equal to 16.5 feet or 5.5 yards.
It is a building surveyor's tool for measuring distance and is particularly useful as multiples of this unit can make up an exact acre. A perfect acre is a rectangle with edges 660 feet and 66 feet - which is 40 rods by 4 rods; i.e. 1 acre = 160 square rods.
The parsec is a unit of length and is used in the Astronomical system of units. It is denoted by the symbol pc.
It is equal to 3.26156 ly (light years) which is approximately 31 trillion kilometres (19 trillion miles). It's used to measure huge distances to objects and planets outside of our Solar System.
It was first brought into use by Herbert Hall Turner (a British Astronomer) in 1913 and was invented to use in calculations of astronomical distances to make it easier in calculations using raw data.