JSTL Introduction

From official document:

The JavaServer Pages Standard Tag Library (JSTL) encapsulates as simple tags the core functionality common to many Web applications. JSTL has support for common, structural tasks such as iteration and conditionals, tags for manipulating XML documents, internationalization tags, and SQL tags. It also provides a framework for integrating existing custom tags with JSTL tags.

In short, it helps us replace scriptlet with JSTL tag, make the page cleaner and simpler, reduce the complexity of JSP page and make it easy to read/understand/maintain.

Reference:

http://www.oracle.com/technetwork/java/index-jsp-135995.html