What is Data dictionary object?

It is the central source of database objects. Basically, it is the dictionary of objects viz. Database Tables, Views, Structures, Table Types, Data Types, Domains, Search Help objects, Lock Objects etc. 

It is tool to create the data base table and data elements

ABAP Dictionary to create and manage data definitions (metadata). ... The ABAP Dictionary describes the logical structure of the objects used in application development and shows how they are mapped to the underlying relational database in tables or views.

Tables,Domains,views,lock object

It is a source of Database and shows the Data Structure and Tables Types.

It is a utility to define objects like tables, views, searchhelp, structure which can be used globally.

In the R/3 product from the German software company, SAP, ABAP Objects is a programming language and part of the ABAP Workbench that allows developers to create and run applications that contain program objects. ABAP Objects includes a virtual machine that will run applications compiled with ABAP Objects language

Database Tables, Views, Structures, Table Types, Data Types, Domains, Search Help objects, Lock Objects etc. 

Data Dictionary is the central source of database objects which describes and manages all the data definations and logical structures used in the SAP System Centrally.

Data dictionary is the central source of the database management system. The main functionality of the DDIC is to create or alter the tables.

Any defined object that resides in the Data Dictionary Repository is a Data Dictionary object. Or any object that can be opened using SE11/SE12 transaction is called a data dictionary object.