BFS (Breadth-First Search) explores graphs level by level using a queue, visiting all neighbors before moving deeper. You use it when finding shortest paths in unweighted graphs or when level-order processing matters. BFS guarantees the first path found to a node is the shortest by edge count.
You'll see this in grid traversal and shortest path problems. If you can explain these concepts in your own words, you'll solve related problems faster under interview pressure.