Prim's algorithm is a method used in graph theory to find the minimum spanning tree of a connected, weighted graph. This tree connects all the vertices with the least total edge weight, ensuring no cycles are formed. The algorithm starts with a single vertex and gradually adds the smallest edge that connects a vertex in the tree to a vertex outside it. As the process continues, Prim's algorithm maintains a growing tree until all vertices are included. It is efficient for dense graphs and can be implemented using data structures like priority queues to optimize the selection of the minimum edge at each step.