Dijkstra
In plain terms
An algorithm that finds the shortest path from a start point to all others.
Going deeper
Dijkstra's algorithm greedily expands the nearest unvisited node, updating the cheapest known distance to its neighbors, until all are settled. It powers routing in maps and networks (with non-negative weights).
Under the hood
Requires non-negative edge weights; a binary or Fibonacci heap brings it to O((V+E) log V). For negative edges use Bellman-Ford; for heuristics use A*.
Examples
GPS routing, network packet routing (OSPF), least-cost pathfinding in games.
Think of it like...
Like water flooding out from a source through pipes: it reaches each junction by the shortest possible route first.