A Plastun or plastoon (Ukrainian, Russian: ïëàñòóí) was a Kuban Cossack foot scouting and sentry military unit. The name derives from the word plast, "sheet" via an expression "to lay like a sheet", i.e., flat and low.
The tradition of foot scouts, vanguard troops and ambushes, together with the term "plastuny", belong to the early Cossack history of the Zaporizhian Sich and mentioned, e.g., by Vladimir Dahl in his "Explanatory Dictionary of the Live Great Russian language". Plastun foot units were introduced during the Russian-Circassian War to guard and scout beyond the "Kuban Line", a frontier in the Kuban plains, against sudden Circassian raids.
Later the name "plastoon regiments" was applied to all Cossack infantry. In the Russian Imperial Army, whole plastun regiments were formed. Normally Cossacks had to buy their horses and horse tack with their own money, and plastuns did not have these expenses. Despite this, regular plastun units were not popular since they did not fit the traditional notion of Cossack pride. Therefore plastun units tended to consist of poorer people.