Guards (Russian: гвардия) or Guards units (Russian: гвардейские части, gvardeyskiye chasti) were elite military units of Imperial Russia prior to 1917–18. The designation of Guards was subsequently adopted as a distinction for various units and formations of the Soviet Union and the modern Russian Federation. The tradition goes back to a chieftain's druzhina of medieval Kievan Rus' and the streletskoye voysko (Стрелецкое Войско), the Muscovite harquebusiers formed by Ivan the Terrible by 1550. The exact meaning of the term "Guards" varied over time.