JSON (JavaScript Object Notation) is a lightweight, text-based data format used for data interchange between a server and a web application. It's an open standard format that uses human-readable text to transmit data objects consisting of attribute-value pairs. It's widely used in web applications for sending data from the server to the client and vice versa. In digital marketing, JSON is crucial for API integrations, configuring web applications, and handling data in a structured, efficient manner.