Wikipedia
Poczet (fellowship or retinue) (plural Poczty) was the smallest organized unit of soldiers in Kingdom of Poland and Polish-Lithuanian Commonwealth from the 15th until the 18th century. The name of a medium or heavy-cavalry soldiers in poczet was pocztowy.
In the cavalry, each poczet was commanded by a towarzysz husarski or towarzysz pancerny. Several Poczets were combined to form larger units such as the Chorągiew ( Company, or more correctly, the equivalent of the medieval Lances fournies).
Pocztowy was an assistant and subordinate of the Towarzysz, in some respects similar to more ancient knight's servant - page or squire. He was armoured like his superior, but fought in the second or third line and was responsible for guarding his back and flanks in a battle.