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 Stores applications 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.
FND_DESCRIPTIVE_FLEXS:Stores setup information about descriptive flexfields.
FND_DESCRIPTIVE_FLEXS_TL:Stores translated setup information about descriptive flexfields.
FND_FLEX_VALUES:Stores valid values for key and descriptive flexfield segments.
FND_FLEX_VALUE_SETS:Storesinformation about the value sets used by both key and descriptive flexfields.弹性域值集
FND_LOOKUPS : Stores information aboutlookup types.
FND_LOOKUP_VALUES :Stores meaning values and codes for lookup types.
FND_MENUS:It lists the menus that appear in the Navigate Window, as determined by the System Administrator when defining responsibilities for function security.
FND_MENUS_TL:Stores translated information about the menus in FND_MENUS.
FND_MENU_ENTRIES:Stores information about individual entries in the menus in FND_MENUS.
FND_REQUEST_GROUPS:Stores information about report security groups.
FND_REQUEST_SETS:Stores information about report sets.
FND_RESPONSIBILITY:Stores information about responsibilities. Each row includes the name and description of the responsibility, the application it belongs to, and values that identify the main menu, and the first form that it uses.
FND_RESPONSIBILITY_TL:Stores translated information about responsibilities.
FND_PROFILE_OPTIONS:Stores information about profile options.
FND_RESP_FUNCTIONS:Stores security exclusion rules for function security menus. Security exclusion rules are lists of functions and menus inaccessible to a particular responsibility.
FND_SECURITY_GROUPS:Stores information about security groups used to partition data in a Service Bureau architecture.
FND_SEQUENCES:Stores information about the registered sequences in your applications.
FND_TABLES:Stores information about the registered tables in your applications.
FND_USER:Stores information about application users.
FND_VIEWS:Stores information about the registered views in your applications.
FND_NODE: 保存节点信息。