JSON and XML are both used for data representation, but they differ significantly in their structure and usage. JSON, or JavaScript Object Notation, is lightweight, making it more efficient for data interchange, particularly in web development. Its syntax is simpler, often resulting in lesser bandwidth consumption. On the other hand, XML, or eXtensible Markup Language, is more verbose and rigorous, making it ideal for document-centric applications thanks to its hierarchical structure. While XML supports metadata and complex schemas, JSON is preferred for APIs because of its ease of parsing and readability by both humans and machines.