Developer file used for Java Server Page (JSP) development projects; saved using XML formatting and contains descriptions of tags, which are used to markup JSP documents; describes the supported tags in a corresponding tag library.
A JSP tag is similar to an HTML tag. For example, a custom tag <loadData> could be used for loading data into a JSP Web page. The custom tag library would have a class handler for this type of tag and the TLD file would describe the tag.
Tag libraries and tag descriptors are included with Java-based Web applications. Often the TLD file is packaged as part of a .JAR file that is located in the /WEB-INF/lib/ directory.