Important FND Tables in EBS

FND stands for foundation tables which is combination of AOL, 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_APP_SERVERS : This table will track the servers used by the E-Business Suite system.
FND_DATABASES : 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.
FND_LANGUAGES : Stores information regarding languages and dialects.
FND_TERRITORIES : Stores information for countries, alternatively known as territories.

FND_CONCURRENT_PROCESSES : Stores information about concurrent managers.
FND_CONCURRENT_PROCESSORS : Stores information about immediate (subroutine) concurrent program libraries.
FND_CONCURRENT_PROGRAMS(_TL) : Stores information about concurrent programs. Each row includes a name and description of the concurrent program.
FND_CONCURRENT_QUEUES : Stores information about concurrent managers.
FND_CONCURRENT_QUEUE_SIZE : Stores information about the number of requests a concurrent manager can process at once, according to its work shift.
FND_CONCURRENT_REQUESTS : Stores information about individual concurrent requests.
FND_CONCURRENT_REQUEST_CLASS : Stores information about concurrent request types.
FND_CONC_REQ_OUTPUTS : This table stores output files created by Concurrent Request.
FND_EXECUTABLES : Stores information about concurrent program executables.

FND_DESCRIPTIVE_FLEXS(_TL) : Stores setup information about descriptive flexfields.
FND_FLEX_VALUES : Stores valid values for key and descriptive flexfield segments.
FND_FLEX_VALUE_SETS : Stores information about the value sets used by both key and descriptive flexfields.
FND_LOOKUPS : Stores information about lookup types.
FND_LOOKUP_VALUES : Stores meaning values and codes for lookup types.

FND_MENUS(_TL) : It lists the menus that appear in the Navigate Window, as determined by the System Administrator when defining responsibilities for function security.
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(_TL) : Stores information about responsibilities.
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_PROFILE_OPTIONS : Stores information about profile options.
FND_SECURITY_GROUPS : Stores information about security groups used to partition data in a Service Bureau architecture.
FND_USER : Stores information about application users.
FND_APPLICATION(_TL) : Stores applications registered with Oracle Application Object Library.

FND_SEQUENCES : Stores information about the registered sequences in your applications.
FND_VIEWS : Stores information about the registered views in your applications.
FND_TABLES : Stores information about the registered tables in your applications