A relatively dense set in Euclidean space 
is a subset 
for which there is a constant 
such that every closed
ball of radius 
meets 
. Equivalently, every point of 
is within distance 
of some point of 
(Moody 2000).
Relative density differs from density in the topological sense. For example, 
is relatively dense in 
but is not a dense set. A relatively
dense set that, with Euclidean distance, is
also a uniformly discrete metric space
is called a Delone set.
