JSTL (JSP Standard Tag Library) is a JSP based standard tag library which offers <c:xxx> tags to control the flow in the JSP page, <fmt:xxx> tags for date/number formatting and internationalization facilities and several ${fn:xxx()} utility EL functions.

Note that JSTL also offers SQL and XML taglibs which enable a declarative manner of executing SQL queries and parsing XML inside a JSP page. This is however discouraged for other purposes than quick prototyping. In the real world both tasks need to be done by real Java classes which are (in)directly controlled/delegated by a Servlet.