The indicated edge is a loop.

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Vertex A is adjacent only to vertex C (since there is no edge from A to B or D).
Vertex B is adjacent only to vertex C (since there is no edge from B to A or D).
Vertex C is adjacent to vertices A, B, and D (since there is an edge connecting C to A, B, and D).
Vertex D is adjacent to C (since there is an edge connecting D to C) and to itself (since there is a loop connecting C to itself).

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The degree of vertex A is 1 (since there is exactly 1 edge going into A).
The degree of vertex B is 1 (since there is exactly 1 edge going into B).
The degree of vertex C is 3 (since there are exactly 3 edge going into C).
The degree of vertex D is 3 (remember, a loop adds 2 to the degree).
The degree of vertex E is 0 (since there are no edges going into E).

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Vertex E is called an isolated vertex (since there are no edges going into it).

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The highlighted edges form path AFED.

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AFEDCBA is a circuit.

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