Software maintenance is the activities perfomed to keep software operational. Those activities are code changes, configuration changes and environment changes
Code changes involves changes to the software of the source code of the software, this is done by developers. This is needed in order to debug de code.
Configuration changes are parameters that control the behavior of the software, this can be set of chains after the software has been built. This is done by tech support or operator.
Environment Changes is the modification of a softwareproduct after delivery to correct faults, to improve performance or other attributes. A common perception of maintenance is that it merely involves fixing defects.
