That is, a graph is connected if there is an edge between any two vertices. In any other case, we say that is disconnected.
We can also have strongly connected graphs.
A graphic is disconnected if and only if its set of vertices can be divided into 2 or more non-empty disjoint sets, such that there are no edges that start in one of the subsets and end in another one.
We call each of these subsets components.
Two Odd Degrees
In such a case, the graph is connected.