Quantitative research, also know as empirical research, refers to what can be be quantified or measured.
Qualitative research focuses on “the meaning of human lives and experiences.” Research study methods include “interviews, ethnographic observation… case studies, grounded theory… and phenomenology.”
Source: Creswell, J. W., Klassen, A. C., Plano Clark, V. L., & Smith, K. C. (2011). Best practices for mixed methods research in the health sciences. Bethesda, MD: National Institutes of Health, 4-5. Retrieved from: https://www.nursing.virginia.edu/media/Best_Practices_for_Mixed_Methods_Research.pdf
When researchers use both a quantitative and a qualitative approach in their studies, it is called mixed methods research.