How much change do you have on you right now? Go ahead, count it.
a) Suppose you check on your change every day for a week as you head for lunch and average the results. What parameter would this average estimate?
b) Suppose you ask 10 friends to average their change every day for a week, and you average those 10 measurements. What is the population now? What parameter would this average estimate?
c) Do you think these 10 average change amounts are likely to be representative of the population of change amounts in your class? In your college? In the country? Why or why not?