ABAP Dictionary stores :
1. Tables
2. Views
3. Types
4. Domains
5. Search Helps
6. Lock Objects
In the development environment or projects objects of the ABAP dictionary can be changed any number of times before activated and made available to the operative components of the system. Objects can have both active and nonn active version in the ABAP dictionary at the same time.
Inactive ABAP Dictionary objects have no effect on the runtime system. The objects can only be activated together when they have all been changed.

Transaction Codes for ABAP Dictionary.
SE11 - Data Dictionary