#### Answer

A path is a sequence of adjacent vertices. Two vertices are adjacent if there is an edge which connects the two vertices.
In a connected graph, for any pair of vertices, there is at least one path with these two vertices as the endpoints of the path.

#### Work Step by Step

A path is a sequence of adjacent vertices. Two vertices are adjacent if there is an edge which connects the two vertices.
In a connected graph, for any pair of vertices, there is at least one path with these two vertices as the endpoints of the path.
In a graph, if there is a pair of vertices such that there is no path with these two vertices as the endpoints, then the graph is disconnected.