Tables (User tables)

USER_TABLES    Lists each table that belongs to your Oracle user.
USER_TAB_COMMENTS    Shows comments on the tables and views.
USER_TAB_COLUMNS    Tells you the names, data types, default values, etc. of each column in each table.
USER_COL_COMMENTS    Shows comments on the columns.
USER_CONSTRAINTS    Gives you all constraints (either single- or multi-column), such as primary key, foreign key, not null, check constraints, etc.
USER_CONS_COLUMNS    Maps constraints to columns (since a constraint can act on one or many columns).
USER_INDEXES    Lists indexes defined on columns (either defined explicitly when creating the data model or defined automatically by Oracle, as is the case with indexes on primary keys).
USER_IND_COLUMNS    Maps indexes to columns.
USER_VIEWS    Lists all views, along with the text used to originally create them.
USER_SYNONYMS    Lists the synonyms and original table names.
USER_SEQUENCES    Lists all sequences, including min value, max value, and amount by which to increment.
USER_TRIGGERS    Contains trigger names, criteria for activating each trigger, and the code that is run.
USER_SOURCE    Contains the source code for all PL/SQL objects, including functions, procedures, packages, and package bodies.

Thanks to my colleague Mr. Hissam for above info.