Software Maintenance is the process of modifying a software product after it has been delivered to the customer. The main purpose of software maintenance is to modify and update software applications after delivery to correct faults and to improve performance.

Software Maintenance must be performed in order to:

Correct faults.
Improve the design.
Implement enhancements.
Interface with other systems.
Accommodate programs so that different hardware, software, system features, and telecommunications facilities can be used.
Migrate legacy software.
Retire software.

Maintenance can be divided into the following:

Corrective maintenance: Corrective maintenance of a software product may be essential either to rectify some bugs observed while the system is in use, or to enhance the performance of the system.

Adaptive maintenance: This includes modifications and updation when the customers need the product to run on new platforms, on new operating systems, or when they need the product to interface with new hardware and software.

Perfective maintenance: A software product needs maintenance to support the new features that the users want or to change different types of functionalities of the system according to the customer demands.

Preventive maintenance: This type of maintenance includes modifications and updations to prevent future problems of the software. It goals to attend problems, which are not significant at this moment but may cause serious issues in future.