LDAP, Lightweight Directory Access Protocol, is an Internet protocol that email and other programs use to look up information from a server.

如果是一个分布式系统，且可能存在不同的ldap，DNS ，NIS等服务器，则宜采用JNDI，it provides a common interface to existing naming services。(类似的还有DNS (Domain Name System)，NIS (Network Information System))

Naming services provide name-to-object mapping, and directory services provide information about the objects and tools for searching for them.

好比图书馆的目录卡片，包含书籍location，书籍名称，以及一些关于本书籍的信息（例如作者，出版社等），用户可以根据location直接查找书籍，也可以根据书籍信息模糊查找。