I'm confused about the difference between the population and experimental units in a situation like the following:
A questionnaire is being used to measure the reaction of two groups of students from a particular American university to a television clip: one group who knows it's in standard definition and another group who thinks it's in high definition.
The population is the group to whom you want to generalize your conclusions. From your limited data, it could be students at that university, all college students or people as a whole. The experimental units are samples from these populations.
I hope this helps. Thanks for asking.