In popular and historical usage, "sharpshooter" and "marksman" are considered synonyms. Within the shooting sports and military usages today, however, sharpshooter and marksman refer to distinctly different levels of skill, which are never conflated. Specifically, in the US Army, "marksman" is a rating below "sharpshooter" and "expert". Four levels of skill are generally recognized today in American military and civilian shooting circles: unqualified, marksman, sharpshooter, and expert. Marksmanship badges for the three qualified levels are commonly awarded to both civilian and military shooters who attain proficiency in shooting higher than "unqualified".
The main difference between military marksmen and snipers is that marksmen are usually considered an organic part of a fireteam of soldiers and are never expected to operate independently away from the main force, whereas snipers are special ops troops who usually work alone or in very small teams with independent mission objectives. Snipers are also often tasked with responsibilities other than delivering long-range fire — specifically, conducting reconnaissance, battle damage assessment and spotting for coordinates/corrections for artillery fire or air strikes. Within the military, marksmen are sometimes attached to an infantry fireteam or squad (where they are known as designated marksmen) where they support the squad by providing accurate long-range shots at valuable targets as needed, thus extending the effective tactical reach of the fireteam or squad.