The Free On-line Dictionary of Computing (30 December 2018):

transitive closure

   The transitive closure R* of a relation R is defined by

   	x R y => x R* y
   	x R y  and  y R* z => x R* z

   I.e. elements are related by R* if they are related by R
   directly or through some sequence of intermediate related
   elements.

   E.g. in graph theory, if R is the relation on nodes "has an
   edge leading to" then the transitive closure of R is the
   relation "has a path of zero or more edges to".  See also
   Reflexive transitive closure.