A measure of CPU speed used by the Linux kernel.  From The BogoMips mini-Howto[1]:

	 :	MIPS is short for Millions of Instructions Per Second. It is a measure for the computation speed of a program. Like most such measures, it is more often abused than used properly (it is very difficult to justly compare MIPS for different kinds of computers).

	 :	BogoMips are Linus's invention. The kernel (or was it a device driver?) needs a timing loop (the time is too short and/or needs to be too exact for a non-busy-loop method of waiting), which must be calibrated to the processor speed of the machine. Hence, the kernel measures at boot time how fast a certain kind of busy loop runs on a computer. "Bogo" comes from "bogus", i.e, something which is a fake. Hence, the BogoMips value gives some indication of the processor speed, but it is way too unscientific to be called anything but BogoMips. 

	 :	The reasons (there are two) it is printed during bootup is that a) it is slightly useful for debugging and for checking that the computers caches and turbo button work, and b) Linus loves to chuckle when he sees confused people on the news.

BogoMips is short for "bogus, meaningless indication of processor speed".  As I understand it, it's not any sort of benchmark, because wall time is not one of the things it's calibrated against; instead it measures the ratio of two of the computer's clocks, or something weird like that.

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BogoMips: How many Million times per second your computer can do absolutely nothing. :-)
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''I heard that the new Q Machine is so fast, it can execute an infinite loop in under 2.48 seconds!''