The JavaServer Pages Standard Tag Library (JSTL), is a component of the Java EE Web application development platform. It extends the JSP specification by adding a tag library of JSP tags for common tasks, such as XML data processing, conditional execution, loops and internationalization. JSTL was developed under the Java Community Process (JCP) as JSR 52. On May 8th, 2006, JSTL 1.2 was released.
JSTL provides an effective way to embed logic within a JSP page without using embedded Java code directly. The use of a standardised tag set, rather than breaking in and out of Java code leads to more maintainable code and enables separation of concerns between the development of the application code and user interface.
For JSTL tutorial please check http://www.roseindia.net/jstl/introduction.shtml