Whenever QTP learns any new object, it stores it in its object repository along with its properties. It is basically used to identify an object and following two types of object repositories are maintained by QTP:
Shared Object Repository: This repository can be shared between multiple tests, but no changes can be made in this repository. It is usually saved with TSR extension and mostly is a keyword-driven methodology.
Local Object Repository: It is linked to only one test. In this repository, the user can easily make the changes, actions, like adding an object in the repository or making changes in an object property, can be done. The objects are saved with the ‘.mtr’ extension.