The name, Mlejnek, originated in the Czech lands (české země) and is derived from the word mlejn which means mill. Variations in spelling are determined by regional dialect. For example, the spelling mlejn, mlyn and mlén are all the same word. Depending upon location in Bohemia (Čechy) or Moravia (Morava), a small mill (diminutive form) might be called mlejnek, mlýnek, or mlének. When used as a surname, Mlejnek appears to be the most common variation in spelling.

The use of the word mlejnek as an object is shown by the Mlejnek z Víru at the Horácké muzeum v Novém Městě na Moravě.  This mill was built by Vincenc Navratil from Vir at a stream near his cottage.  As a plaything for children, it now is one of the featured attractions of the museum.

In earlier times, the mlejn was a daily gathering place where information was exchanged by the local citizens.  Much folklore has been written about the Czech mlejn and also recorded in lyrics of Czech folk music.  Places to eat and places of entertainment carry the name Mlejn and Mlejnek in the city of Praha.