The document discusses user-defined functions (UDFs) in MariaDB. It provides background on UDFs, including their history and pros/cons. It then covers how to install, view, and call UDFs. The bulk of the document explains how to define a UDF in C, including the required API calls for initialization, execution, aggregation, and cleanup. It recommends a book for further reading on developing UDFs and other MariaDB plugins. Towards the end, it briefly discusses deploying a live UDF to solve the problem of matching hotel names from different sources.