A directory service wherein one can hook in various different resource like database,Ejbs,printers etc by providing unique name to each resource so that when one needs to access them one uses this unique name to lookup for that resource. JNDI useful in distributed environment, provides for location transparency.
JNDI is used not only as a lookup point for Java container services (like JMS queues and datasources), but also as a generic interface to many directory services. It is commonly used as a means for accessing LDAP services and sometimes file systems. The JNDI service itself is usually provided by a Java container to the applications that are running in it, but can also be provided by simple providers like Sun's file system JNDI service available from: http://java.sun.com/products/jndi/downloads/index.html#DOWNLOAD12