One way to look at this answer is to think about what qualitative data isn't. Qualitative data does not utilize advanced statistical analysis in formulating solutions in research. Quantitative methods (statistical analysis) will sometimes be used to analyze qualitative data, but in most instances, qualitative data relies on the observable. In simplest terms, qualitative data is data that can be categorized. Social science and humanities research utilizes qualitative data more than, say, medical or scientific research.
An excellent example of qualitative data is data collected from interviews and observations of people in a study. The social sciences use qualitative data, as human behavior has interpretive challenges when it is quantified. Once the information is collected, the researchers categorize the data into sets and subsets of major themes. In some qualitative studies, the themes are reported to the participants, and the participants rank the importance while adding additional comments to the database.
One example of a qualitative study is a school psychologist wanting to know the effect of armed shooting drills on the perceptions by teachers of school safety before and after an armed intruder drill. The psychologist creates a safety survey and conducts interviews with teachers before and after the drill, recording teacher responses. During the drill, the psychologist observes the behavior of teachers. Once the drill is complete and all the interviews are analyzed, the data is reconfigured in the language of participants by theme and then reported to the school staff.
A second example comes from the field of business and marketing. A large retailer has introduced a product. In analyzing the demographic from the sales of the product, the retailer notes that seventy percent of the product's purchases are by female customers. The marketing company wants to expand product sales to male customers. The marketing company calls each of the managers of every retail outlet and asks why the manager thinks the product is not doing well with the male demographic. The response from most of the managers indicates that product placement is the reason for lackluster sales. The marketing company selects a small representative sample of stores and places the product in different locations to see which area results in more purchases by males.
Another example is historical research. Historians gather primary and secondary source materials about a past event. The primary source material is usually in the form of a document, journal, diary, news article, or some other artifact that requires both contextual and interpretive analysis. In historical research, the data set is never complete. New materials surface that alter the original theme from the events. The historian's focus is to create an accurate and truthful representation of an event from the available evidence. Primary source material, by definition, is a first-hand account and observation of an event. It is easy to see how much of the historian's research relies on qualitative data and methodology.