Component
A component, or rather, connected component, of a graph is a connected subgraph of that graph whose vertices are isolated from the rest of the graph. Intuitively, it is a portion of the graph that cannot be walked out of.
Components always include all the edges in the original graph that its vertices participate in. Really, it is the set of vertices that describe each component, because all the edges they participate in are assumed to be included.
An isolated vertex is a vertex with degree \(0.\) That means there are no edges incident to it. An isolated vertex counts as a component all by itself.
No \(2\) components of a graph share vertices in common. Their sets of vertices are disjoint.
When \(2\) vertices are part of the same component of a graph, they are said to be connected because a walk must exist between them.