What does the term "Software Maintenance" refer to?

Software maintenance is the standard IEEE/ISO-IEC-14764 term for the set of activities performed on a software product after it has already been delivered and put into operational use — fixing defects, adapting it to a changed environment, or improving it — as distinct from building that product in the first place.

Applying this definition to the options above, only "Modifying and updating existing software" describes work carried out on a system that already exists and is already in use, which is exactly what the standard definition of software maintenance covers.

Checking the other options against the same definition:

• "Developing new software applications" describes the development phase of the life cycle — building a system that does not yet exist — which happens before maintenance, not as part of it.

• "Enhancing software performance" names perfective maintenance, one narrow subtype among the four recognised maintenance categories (corrective, adaptive, perfective, preventive), not the general definition the question asks for.

• "Managing hardware components" belongs to hardware and IT-infrastructure operations, a discipline separate from the software life cycle that software-maintenance standards describe.