What does the designation hs mean on 22cal rounds that a rifle can fire?

The .22 rimfire is a very old cartridge, going back to the days of black powder. In about the 1930s, cartridge companies began loading higher speed cartridges. These were designated HS to distinguish them from the older era ammo. Most standard ammo today would be classed as HS. Would NOT use HYPERVELOCITY ammo, such as Stingers or Yellowjackets in a firearm marked HS.