In the graph section under corner cases, handbook refers to "disjoint graphs" but I think it means "disconnected graphs"

[vproman]

https://www.techinterviewhandbook.org/algorithms/graph/#corner-cases

Most of the review materials I've looked at refer to disconnected graphs, examples:
https://www.geeksforgeeks.org/bfs-disconnected-graph/
https://algo.monster/problems/graph_intro (paid content)

Googling, disjoint typically refers to edges/paths, but not graphs.