Anything that's qualitative has to do with the characteristics or features of something, rather than its quantity. If you prefer A Wrinkle in Time to another book with the same number of pages, that's a qualitative preference.
Qualitative shows up in scientific writing to clarify that the quality of something is being assessed, not its size or quantity. Scientists often contrast qualitative analysis or data with quantitative facts, information that can actually be measured. Qualitative properties of your house include its coziness and its cheerful color scheme. Among its quantitative aspects are its monetary value and its precise square footage.