FND stands for foundation tables which is combination of AOL（Application Object Library）, SYSTEM, ADMINISTRATOR, MODULES tables and is placed under FND_TOP. Below i have listed few key FND tables that along with the little description of what is it used for :
FND_APPLICATION: 这个表，存储了所有应用产品的信息，每个产品一条记录 Storesapplications registered with Oracle Application Object Library.
**FND_APPLICATION_TL:**TL表，跟语言相关，每多添加一种语言，该表的行数就就有FND_APPLICATION的几倍。Stores translated information about all the applications registered with Oracle Application Object Library.
**FND_APP_SERVERS:**分别显示数据库server、应用server。This table will track the servers used by the E-Business Suite system.
**FND_DATABASES:**存储的是数据库的信息。It tracks the databases employed by the eBusiness suite. This table stores information about the database that is not instance specific.
**FND_DATABASE_INSTANCES:**Stores instance specific information. Every database has one or more instance.
**FND_ATTACHED_DOCUMENTS:**Stores information relating a document to an application entity.
**FND_DOCUMENTS:**Stores language-independent information about a document.
**FND_CURRENCIES:**Stores information about currencies.关于货币的表，好像可以自己定义。
**FND_LANGUAGES:**Stores information regarding languages and dialects.关于语言信息的表。跟本实例没有关系，所有环境应该都是一样的。
**FND_TERRITORIES:**Stores information for countries, alternatively known as territories.关于国家的表。跟本实例没有关系，所有环境应该都是一样的。
**FND_CONCURRENT_PROCESSES:**Stores information about concurrent managers.
**FND_CONCURRENT_PROCESSORS:**Stores information about immediate (subroutine) concurrent program libraries.
**FND_CONCURRENT_PROGRAMS:**Stores information about concurrent programs. Each row includes a name and description of the concurrent program.并发程序的id、名称、更改时间等信息。
**FND_CONCURRENT_PROGRAMS_TL:**Stores translated information about concurrent programs in each of the installed languages.根据语言，并发程序的id、名称、更改时间等信息。
**FND_CONCURRENT_QUEUES:**Stores information about concurrent managers.每个并发管理器（并发队列）的信息，包括客户自己定义的并发管理器。
**FND_CONCURRENT_QUEUE_SIZE:**Stores information about the number of requests a concurrent manager can process at once, according to its work shift.每个并发管理器可以同时处理并发程序的个数。
**FND_CONCURRENT_REQUESTS:**Stores information about individual concurrent requests.单个并发请求的信息，包括请求id、请求名，请求状态
**FND_CONCURRENT_REQUEST_CLASS:**Stores information about concurrent request types.（好像一直是空的）
**FND_CONC_REQ_OUTPUTS:**This table stores output files created by Concurrent Request.并发请求产生的文件，比如pdf的，rtf的，excel的等等。
**FND_EXECUTABLES:**Stores information about concurrent program executables.