Hi Anwesha,
As a simple definition
Table Maintenance Generator is a tool used to customize the tables created by end users and can be changed as required, such as making an entry to that table, deleting an entry etc.
In other words, table maintenance generator is a user interface tool which is used to change the entry of the table or delete an entry from the table or create an entry for the table.
Since this allows maintaining data in tables it is also required to transport that data or records in to different systems in landscape example Quality Stagging and finally on Production and all these changes are send through a Customizing Transport.
The object can be adjusted automatically against another client as part of a Customizing import. This means that the data with differences can be imported from the comparison client.
Hope this helps you understand..
Thanks-
Abhishek