I apologise for the silliness of this question. I ran an e-learning experiment using a class of undergrads. Participation was voluntary, so only half of the class participated.

I know that my sample is the people who participated. Is the population all of the students in that class, or is the population all undergrads in similar course (or whatever I'm trying to generalise the study to)? If it's the latter, then what do I refer to the students in the class as? The cohort?