Primary Caves are formed together with the surrounding rocks. The term Syngenetic Caves is a synonym, the Latin translation of formed at the same time.
When the rock is formed, the space of the cave remains empty. The cave ist formed in the primary stage of rock development, the formation of the rock itself. So the rock does not have to be removed later by a geological process. The geologic term syngenetic is not restricted on caves though.
There are many types of primary caves but their number is very small. Typical primary caves are: