What is a system of units? Write the different types of systems of units.

(N/A) system of units is a complete set of units,both fundamental and derived,for all kinds of physical quantities.
There are mainly four types of systems of units:
$(1)$ $CGS$ system: In this system,length is measured in centimeters $(cm)$,mass in grams $(g)$,and time in seconds $(s)$.
$(2)$ $FPS$ system: In this system,length is measured in feet $(ft)$,mass in pounds $(lb)$,and time in seconds $(s)$.
$(3)$ $MKS$ system: In this system,length is measured in meters $(m)$,mass in kilograms $(kg)$,and time in seconds $(s)$.
$(4)$ $SI$ system: This is the International System of Units,which is an extended version of the $MKS$ system. It is the globally accepted standard system of units.