DFS (Depth-First Search) explores graphs by going as deep as possible before backtracking, using recursion or a stack. You use it when exploring all paths, detecting cycles, or when order of exploration doesn't matter for correctness. DFS uses space for recursion depth versus BFS's for frontier width.
You'll see this in path finding and connected components. If you can explain these concepts in your own words, you'll solve related problems faster under interview pressure.
