For a partial order, the size of the longest chain is called the length.
Partial Order Length
See also
Partial Order WidthExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Partial Order Length." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/PartialOrderLength.html