Final answer:
A case study is a highly detailed description of a single individual used to investigate rare, unusual, or extreme conditions. It involves in-depth analysis through various methods such as examining existing sources, conducting interviews, and direct observation.
Step-by-step explanation:
A highly detailed description of a single individual generally used to investigate rare, unusual, or extreme conditions is called a case study. A case study involves conducting an in-depth analysis of a single event, situation, or individual by examining existing sources, conducting interviews, and engaging in direct observation. It provides a wealth of information but may have limited generalizability to the larger population.