LUPOP for students
Cohort: a closed group of individuals included in a scientific study. Extensive researcher-generated data are often collected for cohorts at enrolment, which are then followed longitudinally with respect to disease or other outcomes.
Population: a group of individuals that is dynamic (open) in the sense it gains and loses members over time, e.g. all inhabitants of a given country or city. In Statistics, the term "target population" is the whole collection of individuals (the “universe”) that is the target for the statistical inference and from which a sample may be drawn.
Register: A digital collection of data typically collected for administrative purposes on individuals for a given population, e.g. all inhabitants of a given country, all individuals that have become ill in a certain disease, all visits to a given hospital.