geometry_dump — A composite type used to describe the parts of complex geometry.
geometry_dump is a composite data type containing the fields:
geom - a geometry representing a component of the dumped geometry. The geometry type depends on the originating function.
path[] - an integer array that defines the navigation path within the dumped geometry to the geom component. The path array is 1-based (i.e. path[1] is the first element.)
It is used by the ST_Dump* family of functions as an output type to explode a complex geometry into its constituent parts.