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

如果是一個分布式系統，且可能存在不同的ldap，DNS ，NIS等服務器，則宜采用JNDI，it provides a common interface to existing naming services。(類似的還有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.

好比圖書館的目錄卡片，包含書籍location，書籍名稱，以及一些關于本書籍的信息（例如作者，出版社等），用戶可以根據location直接查找書籍，也可以根據書籍信息模糊查找。