One of the disjoint subsets making up a set partition. A block containing  elements is called an 
-block. The partitioning of sets into blocks can be denoted
 using a restricted growth string.
Set Block
See also
Block Design, Restricted Growth String, Set PartitionExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Set Block." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/SetBlock.html