The Romanian Carpathians are of global importance in salt tectonics because they host the type locality for the term "diapir." Although there are several historical reviews of worldwide salt tectonics, important aspects of how diapirism has been described and defined in the Romanian Carpathians are missing in these works. Many of these publications are difficult to access, and most are written in Romanian, German, French, or Polish. This paper aims to present in detail the original ideas and to describe the historical development of these concepts. We focus particularly on the work of the outstanding Romanian geologist, Ludovic Mrazec, who defined the folds with piercing core and coined the term diapir.