This has a specific meaning within quantitative market research, originating within probability theory and referring to the population that is researched or sampled, drawn from a target population. In this context, a sample should represent the target population, so that the results may be generalised to the whole of that population.
Qualitative research, on the other hand, does not attempt to derive representative samples. Rather, it seeks to include people or situations within a project that will prove the most fertile, given the nature of the research question; this is known as a purposive sample. In qualitative market research, therefore, the term sample is taken to mean the specific set of people interviewed or observed for a study and makes no technical reference to sampling theory.