Kruskal's algorithm is a greedy algorithm to find a minimum spanning tree in a weighted, undirected graph. Joseph Kruskal first described it in 1956:
Perform the following step as many times as possible: Among the edges (..) not yet chosen, choose the shortest edge, which does not form any loops with those edges already chosen
— Kruskal, 1956
In this case, the shortest edge is the one with the lowest weight.