A "cohort set" is a collection of cohort definitions. In R this is stored in a dataframe with cohort_definition_id, cohort_name, and cohort columns. On disk this is stored as a folder with a CohortsToCreate.csv file and one or more json files. If the CohortsToCreate.csv file is missing then all of the json files in the folder will be used, cohort_definition_id will be automatically assigned in alphabetical order, and cohort_name will match the file names.