BFS (Breadth-First Search)
Graph traversal that visits every node at one depth before moving to the next. Implemented with a FIFO queue.
Guarantees the shortest path in an unweighted graph. Classic uses: shortest hop count between nodes (LinkedIn's "3 degrees"), web crawling, level-order tree traversal, "win in fewest moves" game AI.
Time complexity O(V+E), worst-case space O(V). Competitor: DFS (stack instead of queue, goes deep first), Dijkstra (when edges have weights).