Explain the flood fill algorithm and its applications.

Flood fill starts from a seed point and fills connected regions with a new color. Implementation uses BFS or DFS: check if current cell matches target color, if yes change to new color and recursively/iteratively process neighbors (4-directional or 8-directional). Time O(m*n) for m*n grid. Applications: paint bucket tool in image editors, solving maze, finding connected components, region labeling in image processing.