Bootstorm is a term used in virtual desktop environments where many users start their desktop computers at the same time. Typically this is an office environment when everyone turns up at nine am to start work.
There are several things that you need to be concerned about. Storage networks gets a rise in load, data networks get a rise in load, and the CPU / Mem spikes on the VDI servers.
This is not the same as the CPU storm which occurs when a large number of desktops burn CPU typically where performing an update, patch or virus scan.
With thanks to Tom Gronke in the comments:
The old version of bootstorm was found in an Unix environment where employees were equipped with Xterminals (NCD, Tek, or some other now-extinct brand) that were always left running. After a building-wide or site-wide power outage, thatís when we found the underpowered TFTP server serving out the boot code for these servers couldnít handle a couple hundred simultaneous requests. Itís also where we found end ports that werenít set for spantree portfast.
He is completely correct, how could I forget.