There are varying stories as to how the term "Sharpshooter" came about. Some say that it was popularized during the Americal Civil War with expert rifle soldiers who used a Sharpe rifle . There are also claims that the term has been used by the British Army as early as the 1800 with a group of expert riflesmen, using a Baker rifle.
The term sharp shooter originated with early shooters who were able to hit their targets precisely every time. Today a sharp shooter is a level of marksmanship used in the military to grade a shooter's abilities.