What is a totally ordered sort of sets of a partial order called? Given a DAG, which can represent a partial order and has at least one topological sort.

For example the graph

  &gt;B
 /  \
A    &gt;D
 \  /
  &gt;C


has two topological sorts "ABCD" and "ACBD".

My question is the following:
Is there a name for the following total order sort of sets:

S:  ( {A} , {B,C} , {D} )

The inductive definition is similar to constructing a topological sort: 


Put the all the graph minima (nodes with no input edges) in set #i S: ( {A} )
Remove the graph minima from the graph.  G:= G \ {A}
repeat step 1. with i := i+1 as long as the graph is non-empty


I find this in several computer science domains. For example method selection in CLOS (Common Lisp), a parallel scheduler of a DAG where nodes are tasks and edges dependencies, the list of all enabled sets in dataflow or petri-net model executions, etc.  I haven't found a single nomenclature or even a reference for it though.  It sounds simple and pervasive enough to merit one.
In the context of geometric dominance orders, the standard term is "layers of maxima" (in your case, minima). Obviously, the same term can be used for any partial order.

http://dx.doi.org/10.1007/11785293_34

http://dx.doi.org/10.1007/s00453-004-1082-5