Prim's algorithm, also known as Jarník's algorithm, is a greedy algorithm used to find the minimum spanning tree (MST) of a weighted, undirected graph. A minimum spanning tree is a subset of the edges in a graph that connects all the vertices together with the minimum total weight of the edges, without forming a cycle. In simpler terms, it's like finding the cheapest way to connect all the cities in a network, with the condition that there are no unnecessary loops in the connections.