A merge key in a dataset recipe is used to join related data from different sources within Tableau CRM. By specifying merge keys, users define the common fields between datasets that serve as the basis for combining records. This process is critical for creating comprehensive datasets that pull in relevant datafrom disparate sources, ensuring data accuracy and consistency across the joined datasets. The use of merge keys facilitates the alignment of data based on shared attributes, crucial for accurate analysis and reporting.Reference: https://help.salesforce.c om/s/articleView?id=sf.bi_prep_recipes_join_data.htm&type=5