Semi-structured data is a type of data that does not conform to a strict format but still contains some organizational properties. It often includes tags or markers to separate different elements, making it easier to analyze than unstructured data. Examples of semi-structured data include XML files, JSON documents, and HTML pages. This type of data is commonly used in various applications, such as web services and data interchange between systems. While it lacks the rigid structure of relational databases, semi-structured data allows for flexibility and adaptability, making it suitable for diverse data types and sources.