What does pi 8 mean?

the most likely meaning is ##pi xx 8## or ##pi*8## or ##8 pi##

pi is the English (and other) spelling for the Greek letter ##pi##

##pi##, of course, is the ratio of the Circumference of a circle to its Diameter.

It is about ##3.1416##. (It cannot be expressed with a finite number of digits. That's why we gave it a name.)