A typename is the (string) name of a type of feature in a FeatureStore? or a raster band in a RasterStore?. A single layer of a map will generally be linked to a single data store typename.

In the language of OGR?, a typename is a data layer name. We're not using the term layer in the data context in PCL, it's reserved for talking about map layers. In this way PCL is more like GeoTools? than OGR.