Range of motion is the angular distance and direction your body parts controlled by joints can make while on flex position and the extended position. Every joint in your body have a specified range of motion expressed in degrees and it differs from one person to the other depending with their age and gender. For instance, range of motion gets less as a person gets older.
Stretching your body through various exercises strains and weakness your muscles at the moment but increases your range of motion.

Extended range of motion