What does "chain reaction" mean?

A series of events in which each influences or gives rise to the next event, as in If one person collects substantial damages by suing a company, you can expect a chain reaction of such lawsuits. The term originated in the physical sciences, first (1920s) chemistry and later (1940) physics; in the latter it denotes a process of nuclear fission. By the 1940s it had been transferred to more general use.