The document discusses topological sorting of directed acyclic graphs (DAGs). It defines topological sorting as an ordering of the vertices of a DAG such that for every edge from vertex u to vertex v, u comes before v in the ordering. It presents two algorithms for topological sorting - one based on depth-first search (DFS) and one based on source removal. The DFS-based algorithm runs in O(V+E) time and correctly produces a topological ordering by listing vertices in decreasing order of their finishing times from DFS.