what is Pi?

mathematicians: it's the scale of circumference / diameter of the same circle
Programmer: it's 3.141592655389 by having 2 times accuracy????? O.o
Physicians: it's 3.14159, +- not more than 0.000005
Engineers: is around 22/7
Food Scientists: it's a kind of dessert or food that is delicious and good for health!