The ground set of a mathematical structure is the set of elements on which the rest of the structure is defined. The remaining data can consist of relations, designated subsets, operations, or other specified data associated with the same set.
For example, a partially ordered set is an ordered pair 
in which 
is the ground set and 
is the partial order
(Skiena 1990). A matroid 
has ground set 
and a family 
of independent subsets of 
(Oxley 1993).
