A group or series of case reports involving patients who were given similar treatment. Reports of case series usually contain detailed information about the individual patients. This includes demographic information (for example, age, gender, ethnic origin) and information on diagnosis, treatment, response to treatment, and follow-up after treatment.
In this question, it looks like they didn't really focus on the treatment part of it but otherwise, makes sense
A case series is simply a collection of case studies, typically conservative, that document a similar patient presentation or disease manifestation.