Add a comment to the data dictionary:
  
  Syntax:
COMMENT ON TABLE [schema.]table IS 'text' COMMENT ON TABLE [schema.]view IS 'text' COMMENT ON TABLE [schema.]materialized_view IS 'text' COMMENT ON COLUMN [schema.]table.column IS 'text' COMMENT ON COLUMN [schema.]view.column IS 'text' COMMENT ON COLUMN [schema.]materialized_view.column IS 'text'
To drop a comment from the database, set it to the empty 
  string ' '
  
Example
COMMENT ON COLUMN supplies.part_no IS ’The six digit part number’;
You can view comments by querying the data dictionary views listed below. 
 "Don't let it end like this. Tell them I said something" ~ last words of Pancho Villa 
Related Oracle Commands:
CREATE TABLE
SQL Plus REM statements
Related Views:
COL DICTIONARY DICT_COLUMNS DBA_COL_COMMENTS ALL_COL_COMMENTS USER_COL_COMMENTS DBA_TAB_COMMENTS ALL_TAB_COMMENTS USER_TAB_COMMENTS