The sampling unit is commonly:

The sampling unit is commonly defined as the basic unit containing the elements of the population to be sampled. This could be an individual, a group, an organization, or a geographical area, depending on the research study. For example, if you are conducting a survey on the eating habits of high school students, each student would be a sampling unit. If you are studying the performance of different companies in a certain industry, each company would be a sampling unit.