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.
The fermis is a unit of length in the non-SI metric system and uses the symbol fm.
One fermi is equal to 1×10−15m or 3.9370×10−14 in.
It is used to measure nuclear distances and was named after the Italian physicist Enrico Fermi (1901–1954). It has now been replaced with the SI-derived term femtometre.