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

connected graph

    A graph such that there is a path between any
   pair of nodes (via zero or more other nodes).

   Thus if we start from any node and visit all nodes connected
   to it by a single edge, then all nodes connected to any of
   them, and so on, then we will eventually have visited every
   node in the connected graph.

   (1996-09-22)