what does the pi signify in statistics I have a Ho and Ha pi

what does the pi signify in statistics? I have a Ho and Ha.

pi(infested)= pi(control)

pi in statistics in this context means that is a proportion that you can calculate with a sample

For example: lets say that the sample is N= 50

in this sample there are 20 person infested and there are 30 person in control

p for infested is the proportion of persons that are infested of a sample of 50 and is 20/50=0.4

p for control is the proportion of persons that are in control of a sample of 50 and is 30/50=0.6