Flat file integration is a method of syncing data between applications using human-readable files like CSV, TXT, and TSV, which contain records separated by delimiters. This method involves exporting data from a source system, transforming and validating it, and then importing it into a destination system. While flat file integration supports a wide range of data and is universally accessible, it can be complex to implement and maintain, lacks real-time data syncing capabilities, and poses security risks during data transfer. It is often used when APIs are unavailable or inadequate, and when the data syncing frequency is not critical. The article also discusses the benefits of using Merge's Unified API, which simplifies the integration process by providing a single API to manage multiple customer integrations and offers real-time data syncing through webhooks.