title: Back edges in a graph
body: <p>I'm having a hard time understanding Tarjan's algorithm for articulation points. I'm currently following this tutorial here: <a href="https://www.hackerearth.com/practice/algorithms/graphs/articulation-points-and-bridges/tutorial/" rel="noreferrer">https://www.hackerearth.com/practice/algorithms/graphs/articulation-points-and-bridges/tutorial/</a>. What I really can't see, and couldn't see in any other tutorial, is what exactly a "back edge" means. Considering the graph given there, I know 3-1 and 4-2 are back edges, but are 2-1, 3-2, and 4-3 back edges too? Thank you.<a href="https://i.stack.imgur.com/OqGy9.png" rel="noreferrer"><img src="https://i.stack.imgur.com/OqGy9.png" alt="enter image description here"></a></p>