Which maintenance type is aimed at improving performance without fixing bugs?

The type of maintenance aimed at improving performance without fixing any bugs is perfective maintenance. This maintenance focuses on enhancing the system's functionality and performance based on users' feedback or changing requirements. It is undertaken to optimize the system, enhance its features, or extend its capabilities, thereby ensuring that the software remains relevant and efficient without necessarily addressing existing issues or bugs.

Perfective maintenance can involve various activities, such as optimizing algorithms, refining user interfaces, or adding new functionalities that do not address any immediate faults but rather aim to improve overall user experience and system efficiency. This aligns perfectly with the goal of refining a product for better performance rather than simply resolving errors or deficiencies.