Graph Properties / Features

8. A loop (or self-loop) is an edge that connects a vertex to itself.
   

   The edge begins and ends at the same vertex ($1$ on the graph (left), and $2$ on the digraph), so it is a self-loop. Miriam Briskman, CC BY-NC 4.0.

   \documentclass[border=1pt]{standalone}
   \usepackage{tikz}
   \usetikzlibrary{arrows.meta, bending}
   
   \tikzset{
   vertex/.style={draw, circle, very thick, minimum size=1cm},
   edge/.style={very thick},
   arc/.style={very thick, -Triangle}
   }
   
   \begin{document}
   
   \begin{tikzpicture}
   
   \node[vertex] (v1) at (0,0) {$1$};
   
   \draw[edge] (v1.63) arc[start angle=-50, end angle=230, radius=3.5mm];
   
   \draw (2,1.2) -- (2,-0.5);
   
   \node[vertex] (v2) at (4,0) {$2$};
   
   \draw[arc] (v2.63) arc[start angle=-50, end angle=230, radius=3.5mm];
   
   \end{tikzpicture}
   
   \end{document}