The activity said to occur when yet another big iron merger or buy-out occurs; reflects a perception by hackers that these signal another stage in the long, slow dying of the mainframe industry. Also described as "elephants mating": lots of noise and action at a high level, with an eventual outcome in the somewhat distant future.
In its glory days of the 1960s, it was "IBM and the Seven Dwarves": Burroughs, Control Data, General Electric, Honeywell, NCR, RCA, and Univac. Early on, RCA sold out to Univac and GE also sold out, and it was "IBM and the BUNCH" (an acronym for Burroughs, Univac, NCR, Control Data, and Honeywell) for a while. Honeywell was bought out by Bull.
Univac in turn merged with Sperry to form Sperry/Univac, which was later merged (although the employees of Sperry called it a hostile takeover) with Burroughs to form Unisys in 1986 (this was when the phrase "dinosaurs mating" was coined). In 1991 AT&T absorbed NCR, only to spit it out again in 1996. Unisys bought Convergent Technologies in 1988 and later others.